[Topic split / please don't necrobump]
I can't reproduce on MATE, but you seem to run a Qt-based desktop. Post more info and also try to identify what update (if any) caused the problem.
In the meantime, open a terminal, issue
$ export DESKTOP_APP_I_KNOW_ABOUT_GTK_INCOMPATIBILITY=1
$ telegram-desktop
and see if it helps. If not, continue:
$ export DESKTOP_APP_DISABLE_GTK_INTEGRATION=1
$ telegram-desktop
and post results.