I’m running Ubuntu 21.10 and the distribution only has Audacity 2.4 so I just downloaded the latest appimage.
Audacity ‘works’ but no UI controls are visible. No sliders, no progress bars, no menu selections. I have tried all of the different themes. I manually edited the config file, as the blend with system theme option’s slider is invisible.
I see a similar problem on my system: Audacity 3.1.3 (AppImage) + Ubuntu 21.10. I hope that fix will come soon, because at now some settings like a radio buttons are invisible.
This is what I see with Audacity 3.1.3 AppImage (latest release version from: https://www.audacityteam.org/download/) on Ubuntu 21.10 with Gnome desktop (Wayland):
Audacity is very sluggish on Wayland, so I would not recommend using Wayland.
For me it was caused by a theme mismatch between Ubuntu and Audacity. I had Ubuntu set to dark, but I had to go to Preferences → Interface and then set the theme to match. Tested it out and the same issue appeared when I had Audacity set to dark and set Ubuntu to light.