You cannot create a new page in a multilingual Joomla site. You get 404 page not found.
In a freshly set up Joomla, 4.1.0, only in English, it works.
Please, for the next beta, make it work on a multilingual site.
THE WORLD DOES NOT SPEAK ONLY ENGLISH!?
I have meanwhile set up a multilingual site with Joomla 4.1.0, with the German language. And promptly came the error message 404 page not found.
I then disabled all the plugins that have to do with the German language and then turned on again one by one, each time trying to see if the newly created page opens. All went well until I enabled the language filter plugin. Then came the message 404 page not found.
This only happens when you create a new page. With an existing page everything works fine.
The same happens in Joomla 3.10.6.
So there is an issue with language filter and SPPB 4.