Hi,
thank you for your support. That solved my problems.
For the problem with the php-intl logs I had to update my NextCloudPi
sudo nct-update
To fix the database errors, I followed the steps in this thread:
https://help.nextcloud.com/t/some-indices-are-missing-in-the-database-how-to-add-them-manually/37852/2
Thank you.