apenas execute o telegrama, ele criará automaticamente um arquivo telegramdesktop.desktop da seguinte forma
[Desktop Entry]
Encoding=UTF-8
Version=1.0
Name=Telegram Desktop
Comment=Official desktop version of Telegram messaging app
#path file
Exec=/home/username/download/telegram/Telegram -- %u
Icon=telegram
Terminal=false
StartupWMClass=Telegram
Type=Application
Categories=Network;
MimeType=x-scheme-handler/tg;
X-Desktop-File-Install-Version=0.22