At the moment there are lot of changing parts within Collabora integration… Collabora changed /loolwsd used for ages to /coolwsd which may require change in your reverse proxy configuration (was not the case for me with NC22+traefik)… additionally there seems to be an issue with the richdocuments app 5.0.0 as you referenced already (didn’t dig deeper if both is related).
this one is already a good sign - collabora seems to work.
My observation is Collabora container is pretty slow on start - if you perform any changes please wait 2-3 minutes before you start testing… When I upgraded my Collabora container last time I had the feeling I had to visit Nextcloud configuration page and tick “own server” again (maybe to make NC detect loowsd->coolwsd change). Check this post - NC22+traefik - but maybe it helps: