Check the version number on avr-gdb as of December 2021, it is 11.1. On Ubuntu, the latest version is 8.1 from 2018 which had quite a few bugs. Attempted to build it manually (which failed), so I spun up a Manjaro (Arch Linux) instance to get the latest. Crazy, I know.
Start avarice in a separate window using, then launch gdb in another window: