Incus also removed shiftfs support. You can try VFS idmap shifting that is handled by kernel itself.
Read those two topics: one and two. You simply add shift=true to the device config.
If you’re using LXD, try disabling shiftfs first:
sudo snap set lxd shiftfs.enable=false
sudo systemctl reload snap.lxd.daemon
If VFS idmap shifting doesn’t work for you, you can try setting raw.idmap by hand. Check your users’ UID and GID on host and in container (id -u and id -u commands), then use command:
printf "uid 1000 1000\ngid 1000 1000" | incus config set <container_name> raw.idmap -
Where:
printf "uid <host_user_uid> <container_user_uid>\ngid <host_user_gid> <container_user_gid>" | incus config set <container_name> raw.idmap -