Webfinger/Nodeinfo - yet again


there are numerous posts on this issue, and I’ve read many of them, currently without solution, so maybe someone can help. Please note, my main knowledge doesn’t reside around Linux, HA-Proxy and Apache, so bear with me if I don’t understand some things.

I successfully installed NC 27 (Hub 5), latest as of today, onto bare metal VM with MariaDB, Apache and Redis. I used some tutorials from the net, including this one as main tutorial:
Nextcloud Installation leicht gemacht: Ein Leitfaden für die eigene Cloud - ITS-Farin (sorry, German)

Additionally, I use HAProxy on my OPNsense firewall, to access NC internally and externally via https://FQDN:Port. (note: no /Nextcloud or smth)

So, since this Ubuntu server is exclusively going to be used for Nextcloud, I also put Nextcloud directly into /var/www (so no /var/www/nextcloud), and am using 000-default.conf to change the port and paths. All that seems to work.

The only problem I have is the annoying warning in the Overview Panel:

I know this is a warning only, and not a security issue, however it would really be nice to have it clean.

In the past, I also had an issue with carddav und caldav, and since I’m using OPNsense HAProxy, I was able to solve the issue with http-request set-path to /remote.php/dav.
However, with Webfinger/Nodeinfo, that doesn’t work.

I also found a referencing post on OPNsense forums, that describes an alternative solution with http-request redirect:

However, that also doesn’t help.

Since I am running over external reverse proxy, I don’t believe that any entries in .htaccess or Apache2 config file are relevant, right?

So, this is where I’m stuck at.

Any help?