Can PS5 and PS4 players group together in D3? Is it hard to

looking for a PS5 game that is an ARPG with a strong playerbase

PS5 version of D3 doesn’t exist…it just plays the PS4 version via backwards compatability thus it is the same game with the same player base.

Whether on a PS4 or PS5 it is the same game.

It is only different when the developers release a specific PS5 version like Death Stranding etc but Blizzard have not done so with D3.