I have Betterbird (basically Thunderbird, slight mods) and Firefox, both Flathub Flatpaks. They start extremely slowly, just on my new AMD Laptop. I have Kinoite on old and new laptop, and Firefox and Thunderbird take over 1min to load for some reason.
In the Terminal I just get the output:
ATTENTION: default value of option mesa_glthread overriden by environment.
I use the preinstalled GPU drivers. This is very weird and concerning
Provide output of inxi -Fxz
And use flatpak run com.app.app command on terminal for your app and once opened close that app and see the output you can share that so we can look what is happening there.
I did a re-install of Fedora last week. That may have been a mistake. Since then I haven’t been able to use Thunderbird as I used to. Except for gmail/google, It refuses to connect to my mailboxes (in this case, Verizon via AoL). I can get to them via the browser (Firefox), but Thunderbird is pretty much useless.