I'm back again; I installed the beta version previously to get access to experimental screen resolutions on an Apple M processor: https://psteamcommunity.yuanyoumao.com/app/1567440/discussions/0/4756452715168048068/

I'm seeing that the game wants to update, but it's not showing a filesize for that update, and when I tell Steam to go ahead it appears to start, then complete immediately, then requeue and restart the update process again, and again, without ever progressing anywhere. I'm assuming this is related to my being on a different branch and the update probably not being meant for my version, but if that's true then I would expect Steam to have worked that out, so one way or another there's a bug here.