Try to look for rpgs, most of the time, rpgs tend to be immersive, I can think of Skyrim, Shadow of Mordor / War, pillars of Eternity, the Witcher 3, Dragon's Dogma, Cyberpunk, etc...
The most immersive game must be Red Dead Redemption 2, though, some people find it way too slow, it didn't bother me at all and I even loved this. Many games can be immersive, hell, even Minecraft can be with some mods and a shader.

I can only echo the suggestions for Red Dead Redemption 2.

You should definitely try Red Dead Redemption 2

Red Dead Redemption 2 is (IMO) the most immersive open world game I have ever played.

Subnautica is the GOAT for immersion.

Cyberpunk 2077, Kingdom Come Deliverance I & II, Ghost of Tsushima, Baldur’s Gate 3, Mass Effect series, Fallout: New Vegas, Fallout 4 -

Yeah, the world itself is incredibly detailed and immersive, but the people in it don’t match that level of realism which makes the game less immersive for me on the whole.

Like there’s this jarring disconnect between how alive the environment feels and how flat the NPCs come across. Too often it feels like I'm in this amazingly alive city that's populated by mannequins.

Compare that to something like RDR2, where both the environment and the NPCs feel equally reactive and believable. The most immersive experience I've ever had in a game, hands down.

For me it has to be Red Dead Redemption 2.

I dont think any other game gave me shivers like ME3 when you land on a planet and see reapers in the background destroying everything, be it watching the space battle over the turian homeworld or the ground war on thessia, the atmosphere is amazing.

The stakes feel real, in any other game there would be the nagging feeling in the back of your mind knowing all of this will get resolved in the next 30 minutes and all will be well, not here. Everything is screwed, it wont magically get fixed. The reapers are here and we are doomed, fighting a losing war with no chance of victory

Cyberpunk 2077, hands down.

Kingdom Come Deliverance 1 and 2!!!! Great story, fantastic immersion, very entertaining characters.

My favorite gaming experience probably ever

Dragon Age Inquisition is up your alley.

Also I know you mean no top-down or side scrolling, but “first or third person please” made me think “okay so not second person, got it.”

Kingdom come deliverance

Cyberpunk

Starfield

Fallout 4 modded survival

Red dead 2.

Anything else is worse. Witcher 3 is a super high bar tho

Kingdom come deliverance. You dont get to make your character, but Henry is about as generic milquetoast blank slate as you can get

- Other Elder Scrolls games, I think Daggerfall has the most immersive mechanics out of those.

- Caves of Qud, I think it has one of the most alive worlds in any video game if you go really in.

- Red Dead 2, it lets you do all the roleplay you want, is really fun.

- Kenshi, it feels like you are living in it, and is not a very plesurable place to live.

- Outward, it feels very immersive once you get into it.

- Gothic games, they share a bit of DNA with witcher games, give it a shot.

I would say Subnautica. Having a silent protagonist in any survival game lets you basically put yourself into the world. Subnautica was a game that I constantly found myself being lost in its world.

Dishonored is definitely one of the best immersive sim games I've ever played, along with the Metro series. I highly recommend both! Some other good choices imo are: Pray, Batman Arkham series, Fire Watch, Dying Light, RE Remakes and RDR2.

The metro series. I’m serious. If you want immersion, metro is the king of it. Unpopular opinion here but exodus was the best one to me and I remember sitting in the back of the train smoking one with one of the crew members while watching the train pass by the Russian landscapes, having extremely in depth conversations. Metro games always start really slow but they are so worth it man

Kingdom come deliverance

Death Stranding. I have a feeling that you will fall in love with the game right from the main menu.

Red Dead Redemption 2 still excels in that regard

Horizon Zero Dawn (get the complete edition or the remastered) there are plenty of quests to see or do etc. Like with the complete edition (and the remaster) you will have access to merchants who sell you “metal flowers” ​​“projectors” and “statuettes” cards, well take them and you will have the longest quests in the game because well it is scattered literally EVERYWHERE and as the map is large even without a quest you will always have those to advance

Maybe it’s not the most detailed and gorgeous world— but, Outward, is quite an immersive open world game. It’s just you, maybe a friend, a backpack and whatever you can purchase or find, on a big adventure. It’s got a good mix of survival and combat, it’s difficult and delightful. Night time is actually dark unlike most games. My friend and I have a killer time playing it. I LOVE the backpack mechanic. The game encourages you to drop your backpack before combat so you can dodge and roll better. After you’ve slayed some bandits— don’t forget to pick up your backpack!

Cyberpunk, KCD2, The Witcher 3, RDR2

I know it’s not a popular take but I really wish Elden Ring had an adventure mode. I want to get lost in the world without fear of being ambushed by something that can one-shot me. At 45 years old and working full time, I just don’t have the energy for a game that’s really hard.

Elden ring for sure.

Has one of the most beautiful, dense, rewarding and engaging open worlds ever made.

It very much has a good rogue lite feel to gameplay. You’ll constantly find yourself craving just one more dungeon, peek around this corner, try this Boss once more.

If you’ve ever played Breath of the Wild, it has a similar feel to it. Everything you find, see and do makes you feel like you’re the first person to ever discover it. Me and my friends always joke it’s BOTW 2.

The difficulty is what scares some people but there’s so much content it’s very easy to over level and make the entire game as easy or challenging as you want it to be.

With those criteria, for me it comes down to either Red Dead 2, Witcher 3, or Cyberpunk. Don’t know if I can pick a best one out of those, but I probably lean towards Red Dead because it’s wildly detailed (helps the immersion part) and its story is ridiculously emotionally charged as well.

bro snuck in FarCry 6 into a roster of absolute banger games like Skyrim, Witcher 3, RDR2 and GTA5 💀

Red Dead Redemption 2

OP really put Far Cry in over KCD2, gotta be yanking my pizzle

HORIZON ZERO DAWN/forbidden west

Cyberpunk or KCD2

Horizon zero series is a no brainer . That’s what u wanna play . Also , I didn’t like Valhalla either but was obsessed with odyssey. They’re different. Those 3 games will keep ya entertained for a while

You'll love Odyssey. Closest thing to Witcher 3 that we have.

both odyssey and origins are way better than valhalla, odyssey is probably the best in the series

Kingdom come deliverance

If we talk lowend compatible, i would say baldurs gate 2. The way everything unfolds and intertwines, the tangents you go.... Great storytelling, text etc. 

Next one would be disco elysium. Just following that wreck of a character and the nuances and slow look on him and the world around...

The Kingdom Come Deliverance series. I honestly think i ruined myself by playing the games as now i cant find a game thats as good as them

Morrowind

Kingdom come deliverance, rdr2, Skyrim, kenshi

This can be said for most games being recommended here

Cyberpunk has the most immersive while I’m just walking around Fallout New Vegas is the immersive while I’m playing the character and game Disco Elysium is the most I’ve felt like I’m the one in that world

Probably Red Dead Redemption 2

Dan Vávra has been a bigoted dick in the past and shows no clear signs of learning, but the Kingdom Come: Deliverance franchise is the only one that fills the niche of immersive medieval simulation RPG

Fallout New Vegas

Cyberpunk 2077

Not true open world, but the metro series is the most immersive linear and “open world” series I’ve ever played