depends on what cpu and kind of power supply would be as to what kind of gpu you should pair with it. and then theres the logistics of fitting it in your case and all. i mean unless youre just going for a straight up resolution upgrade, theres no sense of going with a newer gpu if your cpu will also struggle with the game. the bottleneck wouldnt really bring alot of benefit to you in most games, depending on what you are using
if you have a fairly modern i7 you should be good to go, and it might be worth looking into the used market for like a 3060ti or 3070 or a 6700xt/6800xt or whatever you can get on the cheap and that will at least be able to run the game a bit more respectably and you wouldnt have to break the bank. but you have to trust the seller that he didnt mine the card out or whatever. it depends how much money you are willing to spend. if youre using like an older i5 or something youre gonna end up bottlenecked and running at sub 30 fps regardless of whatever gpu you put in there and at that point it might be worth looking at a new build. and if you want a newer generation card, youre gonna have to shell out a fair bit.
id suggest trying a month of game pass just to see if this game can run well enough for you to play. at least before you commit to any serious hardware upgrades. and everybody has their own standards of whats playable and whats not acceptable. if its good enough for you, you might be able to just get by. but right now the 1080 is looking like its going to struggle a little bit, and depending on your cpu that might hamper your potential upgrades. right now they are calling for a minimum i7-6700k or amd equivalent just to be able to play this game. i7-10600k is recommended. so its not exactly calling for a weaker cpu either. i mean if you aint got a decent i7, you're probably not going to ever see 30+ fps on there anyways, even if you threw a 4090 in there.
personally i wouldnt go and commit to any upgrades just yet. we never know if bethesda might further optimize the game and nvidia puts out some better drivers or whatever it is. if its a game you feel like you really need to play, just grab a month of game pass and see how it runs for you. maybe in a while they will improve on the game engine, but for now older systems are really going to struggle with this one. and then theres always the option of buying a series x off someone just to play the game and suffer with the console performance.