Redirection-Problem with HTTPS, HTTP+Port works fine

Hello guys,

i finally got my Nextcloud-Setup running.
I got a Ubuntu-VM running on Proxmox. On that there is docker running with the Nexcloud-App, -Database, a Plexserver and Nginx Proxy Manager. Depending on the (Sub)domain (using coming to my Server, Nginx redirects the incoming HTTPS-requests (on the 443 Port of the router) to Ports 32400 (plex) and 8080 (Nextcloud)

Nextcloud version (eg, 20.0.5): 22
Operating system and version (eg, Ubuntu 20.04): Ubuntu 20.04
Apache or nginx version (eg, Apache 2.4.25): Nginx 1.22
PHP version (eg, 7.4): 7.4

The issue you are facing:

Connecting via a Browser through HTTPS works fine everywhere, but if i want to connect an App (no difference between Tablet, Smartphone, PC,…) via the HTTPS-Adress (e.g. i get the (german) Error Message “Strikter Modus, keine HTTP-Verbindung erlaubt” which probably means “Strict mode, HTTP-Connection denied” and its not connecting.

A workaround that does work is adding another subdomain, opening up the 8080-Port in my Router and connecting the Apps over the, now unsecure, HTTP-Connection adding the Port-Information, e.g.

The output of your Nextcloud log in Admin > Logging:

So primarly i wanted to use HTTPS to access all my data, especially when i’m not in my home network.
Would you agree that using HTTP is too insecure?

Thanks in advance for every hint,
greetings from Vienna!