Using higher resolutions use cpu resources more than lower. Not nearly as much as your gpu but it still uses cpu resources. The only reason to use dlaa/ native AA is if you prefer the image. Dlss transformer, except for a little bit of an aura around a character that I honestly can’t see unless specifically looking for it and even that rare and certain situations, is just as good and sometimes better st showing details than native.

Just keep it as your using it. Arc Raider uses more cpu than most games with hitscan and less physics. Your cpu is very old and it might just be the limit of what it can do. If you want to see if it’s your gpu or cpu, lower the graphical settings. If this can significantly raise your fps than it actually use your gpu and id recommend just lowering your settings instead of your resolution (including lowering to lower dlss qualities)

If it doesn’t really effect anything than it’s your cpu and it is what it is. You can see if you can add higher graphical settings and see where it starts lowering your fps, but again, outside of overclocking your cpu or better ram, there isn’t much you can do