Hmmm, something has gone wrong. When you view communities without parameters in URL, the buttons that let you choose have disappeared.
Compare:
https://piefed.social/c/movies@lemm.ee with
https://piefed.social/c/movies@lemm.ee?layout=list

Edit: it doesn’t seem related to URL parameters actually. The plot thickens.
Edit 2: fixed upstream in the code now; the change will make its way to the website in a day or so. Thanks for bringing this problem to my attention.

I’ve set those 2 communities to default to ‘gallery mode’, and I’ll look into where the buttons have gone (although they only change the temporary view, not the default)