Gaming

I was about to suggest "Balatro" but you don't want infinite dopamine game then play The Binding of Isaac:Rebirth.

Red Dead Redemption 2, Fallout 4, the BioShock series

I want to throw out Mario Bro 3, Tetris, Dr Mario, and Sonic Mania. Just pick up and go, no long term commitment, always fun solo but you can add a friend anytime. Simple but rewarding game play loop.

Wart Under

Sorry to be a soulsborne weeb but I have something like 1500 hours in bloodborne and I still pick it up from time to time

Besides what people have mentioned, you also have simulator type games like SimCity. Though with SimCity, I got bored of the "new" SimCity they released.... in 2013. Either play something like SimCity 4000, or try Cities Skylines.

UT99 so shoot me lol

Football Manager!

One of my favorites is Invisible Inc. Top down tactical game but focused on stealth instead of combat. Its a cyberpunk setting with a stylized art style. You run a corporate espionage outfit, that's just been doublcrossed and exposed. Your supercomputer only has a few days worth of juice so you've got to a few days to get to the bottom of it and rebuild your agency enough to survive.

The levels are procedurally generated and sunce each campaign is time limited you really have to work with what you're able to find each run. You choose two agents to start and can find up to two more to round out your group as you go. They all have different abilities and synergies with each other so lots of combos to explore.

There's also an endless mode thats fun as well, and is different than the campaign since you don't have a time limit. You have time optimize your agents and have time to get your ideal gear loadouts. They also throw more security measures at you as the days progress.

Its super well balanced, and i can't recommend it enough

So maybe don't take this as a real suggestion because it doesn't make sense to be a game with lots of replayability, but I've replayed the everything shit out of FF8. I don't think it's because of the game. It's because of me. Maybe it might do the same for you?

For me, that would be the 3D Mario games (or any Mario game, really).

I have over 70 hours logged into Super Mario 3D-Stars, and that’s just the newer way I’ve played these games.

The Binding of Isaac with all the DLCs. I really mean it. It's the most replayable game I ever played, not only that, but there's tons of mods on the Steam Workshop too.

I don't think any other roguelike comes close in just the sheer amount of things to do and see in this game. I've been playing on and off for years, have more than 500 hours and I still have challenges to complete, characters and items to unlock and item synergies to see.

I gotta get back into Ultrakill, I really wanted to start P-Ranking to get to the big boss fights.

Turbo Overkill is sort of Duke Nukem/Quake strafe boomer shooter with modern schmovement mechanics like Ultrakill.

Also another vote for Prodeus. It's basically a Brutal Doom clone. It's messy and gory and just a tone of mindless fun.

I'm playing Prey right now and it's also a ton of fun trying to figure out ways to do stuff instead of running in all guns a-blazing. Still trying to figure out how stealth really works mechanically.

My first reaction on seeing the title was to name a games that just have fun core mechanics where replaying the game is basically just doing more of the same fun thing, so ULTRAKILL means I'm on the right track.
Prodeus is a pretty good doom clone. Not as in-depth as ULTRAKILL, but nonetheless has fun weapons and your basic doom (eternal) movement/mechanics. Blasting your way through enemies is as fun on the first level as the last. And the Quake games hold up extremely well, and the mechanics are so simple and powerful that you can really have fun replaying and getting better.
Stealth games are also very fun for this. The Splinter Cell series (especially Chaos Theory) are very fun to try to perfect/improve on. Dishonored and Thief as others have mentioned. And Midnight Club is the best racing series for this. You'll have to emulate it, but it's worth it. Completely open-world, and learning the city layout over time is very satisfying.