What I say in this post, I say with love, because this is my favourite game series and I just want to make it better... However I can't ignore the glaring problems with the stealth in Valhalla that are just, flat out, ignored in buglists and the known issues list.
These issues have been here since launch and have had no TLC to make it any better. So here we go:
There's no setup/utility in this game for stealth, ie. Proper smoke bombs, double assassination techniques, crowd blending (that works, or is readily available). You could argue there are smoke arrows and runes that do things like this, but most of the time using them just isn't feasible and will get you detected.
Enemy detection speed is really quick, broken quick. Previous entries had phases of white-yellow-detected, which was great and fair, but this game seems to go instantaneously to yellow/detected even if the enemies cannot see you or saw you very briefly as you passed an open door frame. I don't know if this is intentional, or if it's a bug, but either way it sucks.
Enemies are clumped together and situated in such a way that in some cases stealth is impossible, save for peaking over a roof with the bow, which gets old after 100 hours. This is further exacerbated by the first point, lack of setup makes these situations worse. The lack of a real means of taking out more than one enemy at a time also doesn't help when enemies readily travel in groups of 3 or more. Some people are able to do a janky combo of using the bow and air assassination to take down two enemies in quick succession, but this seems more of a workaround than a mechanic and is very sloppy.
There's no way to disengage combat, once you're in, you're in, unless you run away. It would be nice if we had an option to stun enemies and have them stumble around in, say, a smoke bomb, giving the player an opportunity to hide and return to stealth without having to run away from the conflict zone and come back.
Enemies can detect you through walls, and from across the map. This one speaks for itself, very frustrating!
If one enemy knows where you are, they all do. There have been many instances where an enemy will spot me and the entire camp will run at me, even if they are definitely not within earshot of the enemy screaming.
Hiding spots are fickle, sometimes moving slightly in a bush will push you out of "hidden" status temporarily, even if you're quite clearly in a bush. This mixed with the omniscient enemy detection makes me avoid using cover in any way as it's not reliable and a roll of the dice.
The whistle, sometimes, doesn't work. The whistle is arguably the only real strategic setup you can use in this game for assassinations and whether it works or not seems to be RNG. Usually you have to resort to spamming the button until the enemy walks towards you, sometimes this works, sometimes it doesn't.
Eivor's animations are too slow, there's no quick way to use the hidden blade and it will usually result in a 3-5 second animation, giving the omniscient enemies the chance to spot you and begin combat.
Relying on the bow as the only means of dealing with enemy groups is boring. Especially after 100 hours, the loop of peaking over a rooftop and using the bow to kill one enemy, crouch back down, rinse repeat, can get really old. It would be nice if we had something else that we could use, even if it was niche! Some of the more recent games, such as Unity/Syndicate, had weapons that you could use from range or close-ish to the targets that would give you a sense of accomplishment if you pulled it off without being spotted. Things like firecrackers, coin throws, that sort of thing. It would be nice to see this reappear in the series if it can't be implemented in Valhalla.
The hood coming down in combat is very jarring and irritating, what's up with that - let me keep it up! The animations exist to attack and keep it up, you can do this anywhere in game, so I don't understand why it's absolutely necessary for it to come down during real combat, it doesn't make sense. More customisation in games is very rarely a bad thing, and this one just seems like a silly oversight.
Apologies if this is a common post, but frankly, if they just fixed the problems that people are constantly complaining about then they wouldn't get so many posts about it. It's Assassins' creed after all and they should really listen to these posts, especially if they're recurring.