I could not find anything against systemd-networkd in bullseye.
I did use this page SystemdNetworkd - Debian Wiki. But the last change is from the end of 2019.
I did unmask the services like @monstermunchkin wrote.
systemd-networkd debug log
Sep 24 13:51:13 debiantest systemd-networkd[198]: SELinux enabled state cached to: disabled
Sep 24 13:51:13 debiantest systemd-networkd[198]: Failed to increase receive buffer size for general netlink socket, ignoring: Operation not permitted
Sep 24 13:51:13 debiantest systemd-networkd[198]: sd-device-monitor: The udev service seems not to be active, disabling the monitor
Sep 24 13:51:13 debiantest systemd-networkd[198]: sd-device-monitor: No permission to stat PID1's netns, unable to determine if we are in host netns: Permission denied
Sep 24 13:51:13 debiantest systemd-networkd[198]: Failed to increase buffer size for device monitor, ignoring: Operation not permitted
Sep 24 13:51:13 debiantest systemd-networkd[198]: Bus bus-api-network: changing state UNSET → OPENING
Sep 24 13:51:13 debiantest systemd-networkd[198]: sd-bus: starting bus bus-api-network by connecting to /run/dbus/system_bus_socket...
Sep 24 13:51:13 debiantest systemd-networkd[198]: Bus bus-api-network: changing state OPENING → AUTHENTICATING
Sep 24 13:51:13 debiantest systemd-networkd[198]: Registering bus object implementation for path=/org/freedesktop/LogControl1 iface=org.freedesktop.LogControl1
Sep 24 13:51:13 debiantest systemd-networkd[198]: timestamp of '/etc/systemd/network' changed
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: New device has no master, continuing without
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Flags change: +UP +LOWER_UP +RUNNING +MULTICAST +BROADCAST
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Link 124 added
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: link pending udev initialization...
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Saved original MTU: 1500
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: New device has no master, continuing without
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Failed to get driver, continuing without: Operation not supported
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Flags change: +LOOPBACK +UP +LOWER_UP +RUNNING
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Link 1 added
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: link pending udev initialization...
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Saved original MTU: 65536
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Remembering foreign address: fe80::xx::xx/64 (valid forever)
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: link_check_ready(): link is in pending state.
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Gained IPv6LL
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: link_check_ready(): link is in pending state.
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering foreign address: ::1/128 (valid forever)
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: link_check_ready(): link is in pending state.
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering foreign address: 127.0.0.1/8 (valid forever)
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: link_check_ready(): link is in pending state.
Sep 24 13:51:13 debiantest systemd-networkd[198]: rtnl: received non-static neighbor, ignoring.
Sep 24 13:51:13 debiantest systemd-networkd[198]: rtnl: received non-static neighbor, ignoring.
Sep 24 13:51:13 debiantest systemd-networkd[198]: rtnl: received non-static neighbor, ignoring.
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Remembering route: dst: ff00::/8, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: local, proto: boot, type: unicast
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Remembering route: dst: fe80::xx::xx/128, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: local, proto: kernel, type: local
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering route: dst: ::1/128, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: local, proto: kernel, type: local
Sep 24 13:51:13 debiantest systemd-networkd[198]: outbound: Remembering route: dst: fe80::/64, src: n/a, gw: n/a, prefsrc: n/a, scope: global, table: main, proto: kernel, type: unicast
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering route: dst: 127.255.255.255/32, src: n/a, gw: n/a, prefsrc: 127.0.0.1, scope: link, table: local, proto: kernel, type: broadcast
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering route: dst: 127.0.0.1/32, src: n/a, gw: n/a, prefsrc: 127.0.0.1, scope: host, table: local, proto: kernel, type: local
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering route: dst: 127.0.0.0/8, src: n/a, gw: n/a, prefsrc: 127.0.0.1, scope: host, table: local, proto: kernel, type: local
Sep 24 13:51:13 debiantest systemd-networkd[198]: lo: Remembering route: dst: 127.0.0.0/32, src: n/a, gw: n/a, prefsrc: 127.0.0.1, scope: link, table: local, proto: kernel, type: broadcast
Sep 24 13:51:13 debiantest systemd-networkd[198]: Remembering foreign routing policy rule: priority: 32766, ::/0 -> ::/0, iif: n/a, oif: n/a, table: 254
Sep 24 13:51:13 debiantest systemd-networkd[198]: Remembering foreign routing policy rule: priority: 0, ::/0 -> ::/0, iif: n/a, oif: n/a, table: 255
Sep 24 13:51:13 debiantest systemd-networkd[198]: rtnl: received rule message with invalid family 129, ignoring.
Sep 24 13:51:13 debiantest systemd-networkd[198]: rtnl: received rule message with invalid family 128, ignoring.
Sep 24 13:51:13 debiantest systemd-networkd[198]: Remembering foreign routing policy rule: priority: 32767, 0.0.0.0/0 -> 0.0.0.0/0, iif: n/a, oif: n/a, table: 253
Sep 24 13:51:13 debiantest systemd-networkd[198]: Remembering foreign routing policy rule: priority: 32766, 0.0.0.0/0 -> 0.0.0.0/0, iif: n/a, oif: n/a, table: 254
Sep 24 13:51:13 debiantest systemd-networkd[198]: Remembering foreign routing policy rule: priority: 0, 0.0.0.0/0 -> 0.0.0.0/0, iif: n/a, oif: n/a, table: 255
Sep 24 13:51:13 debiantest systemd-networkd[198]: Enumeration completed
Sep 24 13:51:13 debiantest systemd-networkd[198]: Bus bus-api-network: changing state AUTHENTICATING → HELLO
Sep 24 13:51:13 debiantest systemd[1]: Started Network Service.
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=Hello cookie=1 re
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Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=RequestName cookie=2 reply_cookie=0 signature=su error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=AddMatch cookie=3 reply_cookie=0 signature=s error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_3124 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=4 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_31 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=5 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1/link/_3124 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=6 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/network1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=7 reply_cookie=0 signature=sa{sv}as error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.10 path=n/a interface=n/a member=n/a cookie=1 reply_cookie=1 signature=s error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Bus bus-api-network: changing state HELLO → RUNNING
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=signal sender=org.freedesktop.DBus.Local destination=n/a path=/org/freedesktop/DBus/Local interface=org.freedesktop.DBus.Local member=Connected cookie=4294967295 reply_cookie=0 signature=n/a error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=signal sender=org.freedesktop.DBus destination=:1.10 path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=NameAcquired cookie=2 reply_cookie=0 signature=s error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=signal sender=org.freedesktop.DBus destination=:1.10 path=/org/freedesktop/DBus interface=org.freedesktop.DBus member=NameAcquired cookie=3 reply_cookie=0 signature=s error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.10 path=n/a interface=n/a member=n/a cookie=4 reply_cookie=2 signature=u error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Successfully acquired requested service name.
Sep 24 13:51:13 debiantest systemd-networkd[198]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.10 path=n/a interface=n/a member=n/a cookie=5 reply_cookie=3 signature=n/a error-name=n/a error-message=n/a
Sep 24 13:51:13 debiantest systemd-networkd[198]: Match type='signal',sender='org.freedesktop.login1',path='/org/freedesktop/login1',interface='org.freedesktop.login1.Manager',member='PrepareForSleep' successfully installed.