Steps to reproduce the issue

Try to install a joomla instance inside a container that is just reachable from the internet via reverse-proxy.

Expected result

Installation succeeds after entering administrative credentials and database configuration.

Actual result

A message "A Database error occurred." is shown on top of the installation site.

System information (as much as possible)

Container: Debian Bookworm, Apache, Joomla 4.2.8 from zip download.
Browser: Firefox 110.0.1

Additional comments

I found Firefox showed the javascript installation.dbcheck blocked because of "mixed content".
As far as I see this is because the URL in Joomla.installationBaseUrl was just prefixed
with http:// while I tried to install via https://.

And I could workaround this issue for my installation by replacing in index.php the
data-base-url="<?php echo Uri::root(); ?>" by
data-base-url="<?php echo str_replace('http://','https://',Uri::root()); ?>"

I found following locations where this http originates from.