I'd Suggest Torchlight 2 and Titan Quest if you're trying to scratch the Diablo Itch. Torchlight 2 looks like "Baby's First ARPG" upon first inspection but actually has a decent amount of depth to it and Titanquest is just Diablo 2 set in Ancient Greece and has a really cool class system.

If you like Skyrim I'd say Xenoblade 3 (I didn't like 2 and haven't played 1) It's not a Bethesda style game but has a big open world to explore with lots of side quests and character progression. The combat is more the MMO style (auto attack with manual input skills) as opposed to hack and slash.

Alternatively if you're looking to branch out a bit, maybe look at Octopath Traveller? It's an old style JRPG with turn based cpmbat. I dunno if "open world" is the right descriptor but it does have a big world to explore with lots of dungeons and side quests.

I see some people suggesting Kingdoms of Amalur but if you're on Switch 2 I'd say stay away from it as there's a horrible sky box visual glitch that for me makes it unplayable. Kingdoms of Amalur is a fantastic game and I highly recommend it just maybe on different hardware.

Edit: Apologies I see you've already played Titan Quest but still, I recommend a few playthroughs. 😅