Newbie - Error message: Session expired

Hello everyone,

I have a problem with Matomo. After installing and inserting the code snippet you get this message in the dashboard and everywhere else in Matomo:

Your session has expired due to inactivity. Please log in to continue.

But a new login does not help, the same error will occur.
I have deleted the database and the Matomo folder and set everything up again (website is new)
Same error again.

I also have Matomo running at another hoster, everything works there. The following 2 things are now different:

I am this time at Host Europe
It could be that you have to set something here that is pre-configured at my other hoster.

i have built the websites with .php this time instead of .html, does it make a difference?

Otherwise I can say that the code snippet is included in the head-tag via php, this is also visible in the page source code, so it is delivered correctly.
The page is redirected to non-www and https, that’s what I specified during installation:
Could this be the error? I’m not sure, but I think this is how I specified it with the other hosters and that’s where it works.

Unfortunately I couldn’t find anything by searching with Google, is the error known to anyone?
I am a little bit helpless concerning a solution.

Thanks in advance!

Sorry for the bad english, I used deepl.
Here is the original in german: