Hi,
found the issue!
The problem is that OP is by default configured to use HTTP for communication between apache and the Docker container. This makes OP try to redirect to http which is forbidden for security reasons, so no redirect happens at all.
Pity is that I configured my old installation to use https, so this was overwritten during the update to v8.
To solve this, go to the Administration -> System settings -> General -> Protocol and set it to HTTPS. Save the changes - done.
Regards,
Felix