Hello ;
I guess you are talking about Facebook, or Duolingo shortcut ;
They are linked to chromium-browser, installed via apt.
I openned a terminal as root (command: sudo su -), then cd /usr/share/applications/
I was able to find related desktop file (ls) I removed (rm)
(then, I rebooted to refresh my desktop).
I want also to specify that both chromium (via apt), and google-chrome (via flatpack) was installed.
I do a “apt remove chromium-browser*” to remove this one (as it was duplicate, and linked to shortcut btw).
I hope it will help ;