What was your hardest Steam Achievement or Console Trophy?

If I look at my rarest achievements, they're just annoying grinds.

Looking at my perfect games, Sleeping Dogs definitely was hard because one of them expects you to get 30 in-game gold trophies which basically tested your skills in every area of the game. Also Slay the Spire, it's my favorite game and was loads of fun to master.

The hardest one mentally was Do Not Feed The Monkeys 2099. The game takes 4 hours, it takes you 30+ hours to finish it thanks to a random achievement that can only pop up at the end of the game, you need a new save file every time. The HLTB stats look so absurd.

Honestly i cant remember which one is the hardest, but the most memorable one is offspring fling!. It reminds me of super meat boy (the flash version) due to its difficulty (but i believe it is way easier than that game) and is very satisfying to 100%.

The other one would be binary domain because you need a dedicated group of at least 4 real people (+2 dummies to boost the levels) to get all mp challenges that last for months and then finish a 50 wave run in 3 maps with 4 people. The latter one was fun, but the boosting requires dedication that not many people has.

Fall Guys Infallible. I did it before it was easy.
You needed to win 5 in a row. Took me 200 hours.

I can't really remember that far back when I haven't slept a full night in over a week but recently, the one I was the "most proud of" (and I can tell you that because I rage quit the game maybe 50 times) was "All spots taken" in You Suck at Parking.
When I saw the completion rate on the game, I figured it was because people had abandoned it due to the low multiplayer count and never bothered with the campaign. Nope. Turns out it's fiendishly hard. Honestly ridiculously so.
The kind of games that make you wish the devs would upload a video of themselves completing it because at that point I am pretty sure they did not even try to complete their own game and just amped up the difficulty without making sure it was playable.

Still managed by basically rage-quitting every one of the last 15 levels many many times and trying again days later and managing almost by accident to complete the level.
There are two expansions for the campaign and I tried the first levels. I won't go any further.

payday 2 achievement hunting, i had an excel for it

I don't know about hard but "Embrace the Void" from Hollow Knight is surely one of the achievements I spent the most time on. We're talking hours and hours of failed attempts before succeeding.
The one that I spent most time chasing after, though, is the one from Devil Daggers, but I wasn't as lucky and I haven't managed to get it yet. Seems like I lack proper dedication. I picked the game up and gave up at least 3 times already and I'm closing in to the 60 hours played ^^"

Bullet per minute GrasluTheFirst
Completed Sanngriðr on Hellish.

Only 0.8% Players have it

100% minigame completion in Yakuza 0, the disco minigame almost drove me mad. Sadly full 100% completion for this game is beyond me as it also requires finishing some kind of battle mode I really suck at (meanwhile I spent hours in Mahjong for fun while everybody else seems to hate it).

Also those fucking lightning and butterflies "quests" in FFX back when I played it on PS2, I hope whoever "designed" those will never be allowed to come within 5 meters of a gamepad for the rest of their life.