Streaming via internal IP Adress

Nextcloud version 16.0.5:
Operating system and version Raspbian Buster Lite:
Stream on: Windows 10 and (less important) Fedora
Server Raspberry Pi 4B:

I have a couple of problems, but the main one is that I don’t get my Nextcloud to stream properly.
The most media files do work with the internal Media Player, but some don’t. If I try to connect via an external Player (like VLC or Kodi) with WebDav or directly with http(s) it does not find the server at all (when I use the internal IP Address).
When using the external IP Address, my router stops working and reboots, and I’m not in charge of buying a new one. So I have to go with my internal IP Address.

Is there any way to connect to my Nextcloud Pi to stream with an external Media Player via my internal IP Address (192.168.0.XX)?

Thank you!

Two things: First, I can confirm it does work with Kodi WebDAV. I’ve heard some people have issues but mine streams to Kodi just fine.

Second, many routers do not work well, or at all, when accessing their outside address from the inside interface. This is a bad network practice in general. The solution to this is split DNS where the name resolves to the LAN IP while on the LAN.