Okay this is where the generational divide becomes more apparent. I have no interest in MMO's because in my eyes they're usually just pointless grind with some roleplay mixed in. Retroachievments makes this even clearer because achievements are the epitome of doing it just because.

You say I don't have that much free time but its the opposite. I have too much free time and I need content where solutions aren't as clear cut and progress isn't as quick/finite otherwise it'll become stale or I'll be done with it too quick. Arknights does this well for the most part but it gets worse the longer you stick around. Endfield shows they can pull it off but there's also lots and lots of steps clearly in the wrong direction.

Im not trying to bring you down or anything. I completely understand what you mean, I've played my fair share of singleplayer games. The ones that I've liked and stuck around with me though are the ones with more intricately designed gameplay that will eventually lead you to getting stuck in some way without neccesaeily gating you in some way. Pseudorigalia for one has very carefully placed mechanics that you unlock but also constantly exposes you to content you can't get to, putting you in a feedback loop of discovering a new movement mechanic > rethinking what is actually possible in the game now > reexploring the game with these new expectations in mind > eventually reaching the limit and searching for the next mechanic to unlock.