I saw that already but I was not able to determine the exact solution from that thread.
Somethimes the solution seems to be simply
a2dismod php7.0
a2enmod php7.2
but that I did, the issue has to be somewhere else. phpinwo works fine, ill swicth back to my original nextcloud folder.
Edit:
Can I debug any further why I get a “Internal Server Error” using my netxloud data root instead of that php info test thing i did before? That opcache thing should not be causing this i guess, my 7.2 php ini wasnt touched so far.