SUMMARY: In Wayland only, icons from some (lesser known) applications and Chromium PWAs are missing. STEPS TO REPRODUCE 1. Install git cola or go to twiter.com with Chromium and install the PWA 2. Open installed application OBSERVED RESULT Icon is a white W on a yellow background. EXPECTED RESULT If icon is not in an icon pack, it should fall back to the default icon. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Fedora 34 / KDE Plasma 5.22.4
Yeah, this is an app-specific bug. Best report it to the app developers.
Works with KDE X11 and GNOME Wayland, I don't think this is an app specifig bug.
GNOME has local workarounds for it, but it's still an app bug.