>I want a single player game that gives me the feeling of an MMO with a giant world full of tons of shit to see and do
>aka, a cool RPG (or at least RPG-esque) game where I can create a character and explore a massive, beautiful, varied world with lots of things to find and do

>try baldur's gate 3, a crpg-style game with many small interconnected levels
>try genshin impact, where there's a big open world with fucking nothing to do in it

kek. OP the truth is that people who make threads like this have usually played the games that'll capture the feeling you want. But here are my recommendations
>tainted grail, fall of avalon
Recently released and already been patched to shit. Arthurian Legend made spooky, it's a first-person fantasy RPG. Explore the world, buy a house and live there, find cool shit. slightly janky spooky skyrim.

some of the armour sets you can find or craft or earn remind me of 2000s MMO edgelord sets
>dragon age inquisition
A meme at this point but it has a passable story and "fine" action-rpg gameplay. Use mods to remove timers/limitations that block main quest progress in vanilla. You now have an extremely vast, very varied, quite pretty fantasy world to explore with an insane amount of content in a cool setting.
>oblivion remastered
people have such retarded takes on it, but if you didn't play the original scoop this up and have fun. it's a big fantasy world you can immerse yourself in.