At this point, FNV. Got it a year or 2 ago on PC with all DLC and I'm just now getting to New Vegas after an extended break of not touching the game.

The Celeste mod Strawberry Jam. It's a lot of fun, but I'd be more than satisfied with just getting through the expert levels, which are already at the point where simply watching gameplay of them would kill a small Victorian child, but I'm at just the right level of masochism that this is a tough but satisfying grind. But I've seen what's next, I'm fully aware of the horrors of the Grandmaster levels, and I know I'll hit my upper limit well before 100% completion.

Oxygen Not Included

Super Meat Boy, I think lol

It‘s not my favorite game ever, but it certainly is one of the best games in my library I‘ve too much of a skill issue to completely beat

Factorio. I'm almost at the stage where you can build the launchpad for your rocket, which is technically the end of the game. But the Pyanomod and Space Exploration mods literally add like 1000 hours or more to the game, and I just think I'll probably be dead or society will collapse before I finish those up. The game is literally infinite if you want it to be.

I've enjoyed a lot of Earth Defense Force, but it seems like there's a TON of missions in it. I'm up to 30 or so and have already had some big "This is our epic final battle against the Giant Insects!" moments - and it goes up to 90-something missions, plus DLC.

Well no-one else has said it yet but pokemon.
Over my childhood i played a hell of a lot of Red, Silver, Sapphire and Leaf Green, but i never got close to completing the pokedex.

On my first pokemon (silver) i had three pokemon at lvl100, and the rest of the party was lvl95-98 playing the elite 4 over and over and over with a single pokemon just to get the last few levels (after running out of rare candies) but i never got the dex closer than ~30 pokemon off. Even disregarding the trade or alternate version exclusives and the [practically]unobtainables (legendaries from event codes) it was such a grind to get some of the last pokemon with high evolution lvls and i just never managed to finish that pokedex.

I have come to terms that i will never infact 'catch em all'.

Escape From Tarkov.

I love the game mechanics. But I suck so bad, I'll never get the last quests.

Alley cat

And

Zack McKracken

Undertale. Got two of the endings and got to Final Boss of Murder Mode. Tried 50+ times and decided I’m just not skilled enough to beat that boss. Looked up a vid of the ending and was satisfied. What a wonderful game.

Probably Hollow Knight at this rate. That 112% is a lot.

Probably Skyrim because I haven't finished Dark Brotherhood yet, the last major vanilla faction questline remaining

Dungeon Master. I refuse to use a guide, so even though I've been playing it for almost 25 years, I still haven't finished it. Always run out of food...

Risk of Rain 2 for me. I’ve “finished” the final boss but there’s so much more to unlock and do in that game that I’m not sure I’ll ever be done with it. Absolute blast to play with friends especially when you get those miracle runs where you get all the items that are amazing for your respective classes!

Horizon Forbidden West; I went on holiday just before the final mission and when I went to pick it back up, I discovered that my controller was fucked. Now I'm waiting for the PC remaster because, I still find using a controller slightly unnatural.

I used to like playing hard games but I’m done with them now. I don’t have the skill to complete them without putting a lot of time in and I don’t have the time anymore.

Returnal was fantastic and Sifu was even more fun but I’ll never finish either of them.

Kingdom Come Deliverance probably

Underrail. I love the game so much but every time I hit the level cap I just lose interest completely. Doesn't help that the guy developing it is violently opposed to modding.

I honestly have no idea if I ever finished Skyrim. I finished a ton of quests and became an unbeatable bow hunting dragon killer who yelled all the time. I'm pretty sure I got to some castle where I had to choose a faction and just didn't bother. I explored for a couple hundred hours and never played again. 7 years later I played Morrowblivion and then replayed Oblivion (I couldn't get Skyblivion to work if I remember right). I've debated playing VR Skyrim, but I don't want to repay for the game.

A mod, not a game, but Terrafirmacraft.

I deeply love every part of it, except the ore prospecting system. I always use commands to find my first copper vein because I find it so grindy otherwise. Doesn’t help that the vast majority of TFC’s progression is locked behind copper.

So I guess technically I’ll probably never complete the game legit.

Probably shiren the wanderer, it's a pure roguelite so you can't brute force it like the more forgiving roguelites with permanent upgrades, but I only play in short bursts and always forget stuff when I finally play again.