Recently, I did a regular upgrade on 20.04. After a reboot, the systemd-networkd is activated and enabled which I never do. I have been using NetworkManager to setup the static IP. Now, it doesn't work anymore (no nm-applet, no nm-connection-editor). Instead of using my static IP settings, dhcpv4 picks up the address for me. When I check if the dhcp client is running, nothing is found ( ps aux | grep dh ). Follows many suggestions to switch back to NetworkManager but nothing really work.
I have had a similar problem. I am running an ethernet LAN with 11 computers of various ages, with several in a dual boot mode with Windows XP thru 10, and all 6 general flavors of Ubuntu along with Zorin and LinuxMint (for testing purposes). Up through 18.04 LTS (bionic beaver), have had no LAN issues. Upgrading to 20.04 LTS (focal fossa) wiped out share file communication with any Windows machine, and any Linux machine not running 20.04 upgrades. Tried several fixes posted online, but nothing really worked. Eventually gave up and reloaded 18.04 versions. Any help in understanding and/or fixing this problem would be appreciated. I am hoping this is improved in 22.04.