What GPU do i need

I've been out of the game for a while because i had a successful build with a gtx 1080 and high sierra that was doing it for me

been looking at what gpus i could buy to update my os but i can't find much new info that is not at least 2 years old: Nvidia is not supported after high sierra and amd is not supported after the 6600, 6800 and 6900.

any help would be much appreciated

thanks in advance