update: I used these instructions to install WP:
https://codex.www.ads-software.com/Installing_WordPress#Detailed_Instructions
…and didn’t get any error message until I opened the main page
I also checked the url in phpmyadin, the line read
siteurl Y 1 https://www.iroke.de/wp
which is correct I believe.
I also looked at similar support requests, like
https://www.ads-software.com/support/topic/33651
but since I don’t use permalinks, my problem seems to have a different reason.
