405 Propfind error after changing PC

Hi All,

I have a nextcloud installation running now for some years and syncing files, mails and calendars without any problems to Android phones and Win10 PCs with Outlook and Caldav installed.
After changing one PC now, I can’t sync the calendar any more.
I used the same settings than in my old PC (the old one can still sync) but on the new one I always get a 405 error ‘Propfind is not allowed’.
Everything I can find for this issue is check the apache/NGinx setting for example Rewrite settings.
But because everything is in order and working here, I wonder if I have to reset something on the server to get the sysnc running with the new client, but I have not found anything here.
Someone has an idea, what to do here?