Others have mentioned Elder Scrolls, but nobody recommended Daggerfall yet, so it’s one of my picks. Yes, the 1996 game, which you can play on Unity for a much, much better experience overall. Since the game is free, you don’t need to pay a thing. Combat won’t feel good, tho.
If you enjoy space games, X3 Albion Prelude might be a good option. It’s “open world” in that you can go anywhere right from the start, but the main gist of the game is to get rich so you can get the capital ships. Ship to ship combat is fine, each ship class has strengths and weaknesses. It has a learning curve and can feel needlessly convoluted at times
Kingdoms of Amalur isn’t really open world, but its combat is awesome. Get the original, non-remastered version, and it should run on your stronger PC, hopefully.