Just to add some even longer time goals to the other replies: you could get all achievements for games that have them. Though some of those, like the ones for Civ 6, are excessive. It could give you ideas or shorter term goals to work towards, then you can decide if you’ve had enough at any point before 100% if things get too BS.
Three games came to mind just now, for slightly different reasons.
Similarly to others, just for feeling good: Earth Defense Force (whichever release, really). While it’s great to have a challenge in the missions, getting through the game, finding a good mission to farm weapons on, then using those fun weapons to destroy horses of insects and aliens is just so fun. And some missions can feel a bit BS with the weapons you might have available normally.
I would also actually say Baldur’s Gate 3. I know a lot of people enjoy the tactical side of things, but my opinion is that the DnD 5e ruleset kinda just sucks for a video game. I play it as a TTRPG, it’s fine. But I found rolling badly in something my character’s meant to be good at just so frustrating. This let me actually explore the story and world my own way, which was way more fun to me than restarting combat because I got unlucky.
That one might be controversial, but I was also speed running completion because I wanted to know conclude the story and see the world, but something about the game just didn’t click for me.
And finally, because I think it’s a fantastic game that deserves attention (with the best soundtrack I’ve heard in a while): Rabbit and Steel. It’s a brutally hard roguelike bullet hell that’s based on dungeon raid boss mechanics from FFXIV (which I haven’t played, but that’s what everyone says). The difficulty will make you want to not play it, and for me stuff only really clicked once I unlocked my penultimate class. I can now heat Hard fairly consistently, but it has taken a lot of runs to get there. No shame in admitting that those started from Cute and Normal and involved me grinding out all the unlocks by charging through Cute difficulty.
So really, the summary of this far too long reply is: just lower the difficulty when it’s frustrating or keeping you too much from getting to the fun stuff. You can always try again on a higher difficulty later.