I think your issue is documented here: https://github.com/nextcloud/server/issues/45033
I am getting an error that my htaccess is not working and saying my data directory is probably accessible from the internet. My htaccess does seem to be working, urls are rewritten properly, my .well-knowns work, etc. and my data directory has been outside of the document root for years. I just opened a topic here as well. I guess this is what I get for being bored on a Sunday and deciding it was time to run some updates. My webui wouldn’t show 29.0.0 and that should have been my clue to just wait but I decided to run the upgrade from cli anyway.