Also noticed this broke a while back via https://www.isbetabroken.com, but mentioned in T351131#9329796 too:
See related: T351131: Creating a Wikistory on English betacluster results in a 502 error, T350353: Parsoid instance on beta not accesible from restbase CI/dev envs
See previous: T246833: Parsoid/RESTbase seems to be unavailable in Beta, T267686: [Beta cluster] "Error contacting the Parsoid/RESTBase server (HTTP 500)" appears while trying to save an edit with VE/ reply to a comment using the Reply tool, T241247: Beta Cluster RESTbase is down? (503ing)