The first Digimon game I remember playing was Digimon World 4, and the second one was Digimon World: Data Squad. I remember playing as Dorumon in the former game, and not getting that far in the latter game, though I saw my brother get way further into the game than me.
I have a very distinct memory of the original Digimon World being rented for me as a kid. I couldn’t figure it out but my dad played it all night.
Did you see him get Numemon? That Digimon seems infamous for digivolving into if you don’t know the game much.