Apparently native notifications (i.e notifications provided by your DE, rather
than drawn by the app) for Telegram need to be turned on by compiling against
libappindicator3-1 and making sure that TDESKTOP_DISABLE_GTK_INTEGRATION is not
set in the packaging.

See how Arch fixed this here:
https://git.archlinux.org/svntogit/community.git/commit/trunk?h=packages/telegram-desktop&id=3f47bddefd3b06f0c816c1f88ad78318d2c11763

I just migrated from an Arch-based distro, where the native notifications are
used and they're much nicer than the app-drawn notifications. I did not notice
any bugs after more than a year of use. openSUSE should consider enabling
Telegram's native notifications, too.

For more information, see
https://github.com/telegramdesktop/tdesktop/issues/3831