I just can’t find a decent email client that looks like it’s from the last 20 years. Geary and Evolution both appear to be pretty modern but something about using Gmail with a Yubikey just doesn’t work and neither of them will connect to my account. Both on Fedora and OpenSUSE. Thunderbird works but it’s so old fashioned and Betterbird doesn’t look much better. What’s everyone else using?
Thunderbird. Idk what you mean by old fashioned. It works fine, and you can style it with gtk themes.
On Android I use K-9 Mail, which looks modern to me.
I mean everyone has their preferences, but personally I don’t use email clients because I want to look at something pretty—I use them to read my emails. Thunderbird mostly matching my gtk theme is more than enough for me.
I don’t know if you were aware of this but K-9 Mail has joined up with the thunderbird developers and will at some point transition to thunderbird for mobile devices