No rule for this one
No ending or word group predicts the article of Angebot. Learn it as a pair and say it out loud: das Angebot.
das Angebot
It's das Angebot. Angebot is neuter, plural die Angebote.
Heute ist Kaffee im Angebot.
Coffee is on offer today.
No ending or word group predicts the article of Angebot. Learn it as a pair and say it out loud: das Angebot.