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.
Digimon World 1 on PS1. I still have the game guide and remember slowly figuring out how the evolution mechanic worked, by trial and error. Still love that game. Now there’s an evolution guide online that’ll help you get any mon you want.
FWIW, you can trust any information for that game posted by SydMontague. He knows that game (and most, if not all digimon games) inside and out.
https://www.phoenix-staffel.de/digimon/DigimonWorld/evolution.html