When we were there a couple of weeks ago all of the RV Parks/hook up sites in the park were closed due to Covid -19. We did see some campgrounds inside the park that were open but they appeared to be strictly off the grid.
Everyday we were there the lines seemed to get longer at the entrances. By the time we left on day 6 the back up at the south entrance was looking like an hour or more as people kept streaming north to the park from Grand Teton.
I cannot imagine what Yellowstone looks like in July and August and I can assure you I will never find out. :S