Looking for high intensity/failing matters kind of games (single player)

If you liked Fallout 4, try The Outer Worlds. It's basically Fallout in space featuring everyone's favorite thing: capitalistic hell. Maybe the AI in that one will be more your style.

Visage and Darkwood are very good atmospheric horror games. Blair Witch is decent too but it's very much a horror walking sim. There's not a single jumpscare in Darkwood, but the other two might not be up your alley. They are good though if you wanna check em out.

Hellblade: Senua's Sacrifice will be a game I'll never stop suggesting (at least until the new game drops). It's a souls-like game where you're just trying to stay alive in what's essentially hell while you experience your character's psychosis and relived traumas.

Soulslikes are kind of an obvious answer for single-player games where failing matters. The intensity comes from the challenge and between checkpoints sometimes being far apart and the possibility of losing resources on death makes death matter (at least at times).

Many Diablo-esque ARPGs has "hardcore" modes where your character dies permanently. I know at least the Diablo games and Path of Exile do.

Give Dark Pictures Anthology series a try, I hate jump scares too personally thinks it’s a low tier horror element, but the eerie feeling buildup is good in the series. Also Control, Alan Wake, Quantum Break from Remedy studio!

Getting Over It is different than the other games you've talked about but I think you might like it.

Outward has certain quests where if you don’t finish on time an entire town can get sacked by bandits. There are other quests that rely on you finishing on time with pretty harsh consequences.

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Shadow Tactics / Desperados 3 / Divinity Original Sin 2

you're looking for modded stalker, Anomaly stalker more precisely.

But honestly, a lot of games can be like that if you check the little "ironman" setting, i'm gonna list some challenging game where fails matter.

Xcom 2 : Iron man or not your Character can always die, and when they do they're lost forever, and you do get close to those punks over time, and in one crit, it's all over. Highly recommended, do not ironman at first it's difficult enough without the one save/ save deletion of ironman.

Darkest dungeon (1) : same as above you get some guys kit them up spend ressources on them and you send them on missions, make enough mistake and they're down forever, spent hundreds of hours on this and xcom, entering the final dungeon might give you conniptions.

Mount and blade (Warband/Bannerlord) I suggest playing in ironman from the start so you can't run away from your awful leadership, manage your army roam the continent make war, recrut heroes train them, lose a battle, all your heroes are lost to the wind, (they aren't dead per say, but finding them again is very time consuming) all the mooks in your army are dead, you villages and towns vithout defense will you wait in a jail, nice!

Kenshi : Open world dead meat simulator, imagine a open world where no matter what you do, or where you go it's only different flavor of "deadly" it's like if you start a game and if every area is lvl 70 minimum, that's playing kenshi, go the desert, you gonna get eaten by skippers they run way to fast on sand for your little legs, you might mercifully be found by slavers and taken into custody for... a while, and being a slave isn't a waiting game, you play as a slave, until you escape, or you die. So if not the desert, maybe the bog, nope, Blood spiders are hidden everywhere and will take you limbs from limbs, foglands? Fog people are always hungry and they hunt in group, main trading route? High lvl Marauder will leave you with nothing to your name. Kenshi can be fun, in a masochistic way, do play on ironman though, savor your end.

Maybe a bonus one, while not at all as painful as the others, Nioh 2 expect you to have great skill, if you don't you're gonna die, a lot, and while there isn't truly a punishment for dying (a part from the Soulslike standard of losing all held XP) Nioh 2 is a great punishing game, but once you master it there's none that can compare to it's combat.

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Try Stalker Gamma my friend. Its a mod pack for Stalker Anomaly. It's fun and highly customizable as well. If you want to satisfy that itch of survival you can try this with or without its ironman mode.

Project zomboid? It’s prema death and you basically won’t survive for more than a few weeks until you really get the mechanics of the game down

Darkest Dungeon might be up your alley. Assemble a group of heroes to plunge dungeons for your benefit, but they will have to cope with the insanity they see beneath. There is a full fledged stress system which can give them negative quirks that affect gameplay and can lead them to having a full psychotic breakdown. The game is as much about combat management as it is about stress management. There is also permadeath.

If you like more interactive movie like games play detroit: become human. It is very intense in some parts but calm down at others. Its a really immersive single player game where your choices actually matter, and you can basically shape your own personal ending

the outer wilds

its has that subnautica "scariness" going for it