This is a known issue (tracked at https://bugzilla.mozilla.org/show_bug.cgi?id=2007074, as mentioned by a previous comment). A fix has landed in Thunderbird Daily a couple of weeks ago, and should be released in Thunderbird 154 which comes out next month.
It's been an ongoing issue since the beginning of the year, at least on Linux. Since you're using Ubuntu (which is based on Debian), you may be using an older or an LTS version.
https://bugzilla.mozilla.org/show_bug.cgi?id=2007074
The year of Linux desktop will come after the desktop is no longer relevant, but I'll be honest, I've been AI-pilled, and it's never been a better time to run a Linux desktop. Instead of going sleuthing every time I hit a papercut that previously I'd have spend hours consulting a how-to or a wiki to find the subsystems and config files to fix the problem, I can now just describe the problem to an AI agent that runs around on my system that just fixes it while I go off and do something else.
I'd love to see a screencast of this working if you're so inclined one day to make a walkthrough. If it's mostly walking away, that's even better because you could show the prompt and a before/after of it working. (Just a casual observation, and less of a request, not trying to assign work :)
I've seen so many people claim this is the future we're living in, but I've never seen it actually work as described. It's always more hand holding than I'm willing to put into an llm