I have a shaky Internet connection and my router regularly disconnects from the Internet. When I try to reconnect I get an error message: "IP configuration was unavailable". Then I need to do full system restart in order to connect. Any ideas?
How about giving some more info about, say, which network manager you're using among other things?
I use NetworkManager (https://wiki.archlinux.org/title/NetworkManager).
MB - Gigabyte Aorus Master Rev. 1 X570
Router - Generic ISP
Firewall - Portmaster
Looking up "IP configuration was unavailable" gives a lot of promising results, here are some:
https://access.redhat.com/solutions/7002283
https://askubuntu.com/questions/1458105/internet-access-constantly-dropping-out-ip-configuration-was-unavailable-un
Does restarting NetworkManager (instead of rebooting) solve the issue?
No, it does not solve this issue. Only full system restart solves the issue. I use a wired connection, after a router disconnection I can connect using Wi-Fi but not with a wired connection.
I'd first try another manager (such as connman) first, to make sure where the problem lies. If connman works, get back to NM and switch to static wired configuration.