Probably just me but...

I like to play some older classics lately, so maybe go in that direction? Doom or Blood have proper source ports now and they work very well on new computers along with proper scaling and modern controls.

to me as of right now fortnite is the best you can get, considered its free and it has such a huge quality, the community and devs are also great

Same with me, im lost and looking for good singleplayer games because i actually dont feel playing games anymore entertaining.

You could try to play some strategy game such as the Sid Meirs games or Crusader Kings, can get you hooked and take up LOTS of time.