Bakers Hole 3 miles north of West Yellowstone is nice. Some electric and some not. First come first served, if getting there 9-10am you can usually find a spot.
Rainbow point a little father north has first severed and reserve able, some electric and some not. Last 2 miles are rough road but ok if going slow.
I was in Yellowstone 10 days ago. Crowds were about the same as other years Just US residents but still lots more campers because of the virus.
Keep checking the reserve line every few hours and good chance of getting lucky, I did for both Yellowstone and Rainbow Point and got sites at both. People still cancel. I got my site in Madison campground 6 days before we left.
Very few seen to take precautions for the virus seriously, not many mask but where they are required. We were carefully and kept a few feet between us and others. No issues other than I dislike crowds. Wasn't for grand kids wanting to go there I would not go.