The biggest requirement, imo, is probably just having an SSD for the game. There's a LOT of pop ins and textures that just don't load until a few minutes later. It does have a "slow HDD mode" but it hasn't really done much from what I can see.
That's pretty normal for modern AAA games. There's just a lot of texture streaming going on and that requires a lot of bandwidth that HDDs don't have. You can be lucky if it is just blurry textures & pop in and not also strong stuttering.
I've gotten away with even harder to run games on a HDD but even if it is on an SSD, I've found it to be inconsistent plus only BG3 acts up compared to everything else I have going.
It does run on steam deck (though at lower settings with FSR to get 40 mostly stable).
Open world games with some complexity generally take a decent amount of power. You have to load a good number of surrounding objects at any given time, with a pretty wide view on the zoomed out view. There are also other characters/animals doing stuff, environmental effects, and a healthy dose of passive checks on the environment against various traits of your party to see if your character identifies any of the secrets all over the world.
Support the Steam Deck, Valve is doing everything right. Right to repair, virtually all parts replaceable, Linux, Rma's to name a few. Not to mention it's a monster of a small machine, it could very well be a desktop replacement as well as a portable gaming system.
One of my coworkers got one recently and absolutely loves it. I really want one, but I’m waiting until the next version eventually comes out, since the current one is slightly too heavy for me to hold easily.
I too am waiting on the next version. I need a new phone and laptop before I can think about a steamdeck. So hopefully a new one will be out by the time I am ready to buy it.