How to configure firewalld on the host to be able to access "routed" containers from the internet?

LXD
2

Try to repeat the same filter commands with the option -i as well (for input).

Alternatively, try to use a rule like this, which enables forwarding for all the interfaces, in both directions:

firewall-cmd --permanent --direct --add-rule \
    ipv4 filter FORWARD 0 -j ACCEPT
firewall-cmd --reload

There are some more details in this section.