This may mean that the icons are stored in the Telegram Directory instead of the system Icon Theme. You can check this easily.
Otherwise, the icons in question may be in /usr/share/icons/hicolor/scalable
My TG is installed as a binary from their website. Its folder contains only two binary files.
Browsing for other TG folders I didn't find anything containing icons.
Hicolor folder also didn't contain anything related.
To me it looks like its a bug in Zorin's taskbar notifications code, but lets explore other ideas, if any...
Can anyone using Zorin 15/16 with Gnome confirm how this badge is looking at their end?
Yes, already explored that and even contacted the TG devs - they say its broken on system side, which might be true, cause the same combo of TG and icons works without problems on other distros.
I've also used official zorin feedback to share the problem - so the zorin devs get aware of it.
Finally, since some time has passed without betterment, decided to look for help here on this forum.
Asked for help on Zorin's unofficial TG group and badge is working for others.
The difference was theme and resolution. I have hidpi 4K, others were on FHD.
So we got a troubleshooting vector specified a bit more.
The updater popped up showing some Zorin OS updates today, 22 July (CST) that included:
Changes for gnome-shell-extension-zorin-taskbar versions:
Installed version: 40.16
Available version: 40.17
Version 40.17:
Fixed notification badge sizing on 200% scaled displays
Please run your updater app, or from terminal run: