On my Dell laptop running 18.1 Zorin, telegram has decided to not manifest after clicking the icon on the dash. I have re-started, then uninstalled and re-installed from the software database flatpak. Nothing. Very similar to the Firefox/Zen/Librewolf issue i went through recently. I notice that my other machines do not have this issue, so maybe I should do an fsck ?
Try it with
rm -rf ~/.cache/fontconfig
fc-cache -fv
and then logout.
It may be that you have to repeat the commands if you use a chromium based browser until a fix will coming soon for the browser.