Thanks for your reply. I think somewhere between 10.3.2 and 10.9.1, the OC code changed so that it won’t following symlinks when searching for config file.
In my previous container, I symlinked the config directory to my external volume that was mapped to /mnt/data. I did that so I could update the config (took a while to get proxy stuff to work) and more easily back up my OC configs.
I removed the symlink in my container and replaced it with directory and config.php and OC worked.
Also, occ upgrade script seems to have been run as part of initial container creation. That implies that that branch of code properly read my config file to get the DB parameters to run.
What OC logs are you referring to? I looked at $dataDirectory/owncloud.log and did not really see much to use for debugging.
The giveaway should have been that when I edited my symlinked directory config.php to increase debuglevel in logs, nothing ever changed.