Something must be broken with your GTK theme because it works fine with the default Adwaita theme. I’d suggest opening an issue in your theme’s issue tracker. This kind of issue also happens often in other apps too if using third party themes.
mmm, I try with others themes and I always see the “square blocks” instead of buttons. It’s a fresh install of Fedora 34 (yesterday) and I did not do a lot of tweaks. I’m going to try with the live USB of Fedora 64.
Lol it’s crazy, I just did a new installation of Fedora 34 on my new laptop (Thinkpad P14S AMD). All I did is a dnf update and the installation of Geary -> same issue. How can it be possible?
Your flat version of geary is directly from Gnome Software (what I did) or via the Flathub website?
This is visilble with Geary from the Fedora RPM repositories AND the Fedora flatpak repository, but not the Flatpak from flathub.org. The FP from Fedora uses a spectail F34 runtime which is - this is pure guesswork - similar to a f34 install and thus shows the same issue