Need help nextcloud talk always show blank and fail to show video

[Mornsgrans]

There are a few good guides in internet (search for: “nextcloud talk install turn server”).
One is:

HowTo: Setup Nextcloud Talk with TURN server

Background The configuration of Nextcloud Talk mainly depends on your desired usage: As long as it shall be used only within one local network, nothing should be needed at all. Just verify that all browsers support the underlying WebRTC protocol (all famous ones do on current versions) and you should be good to go. Talk tries to establish a direct peer-to-peer (P2P) connection, thus on connections throughout the local network (behind a NAT/router), clients do not only need to know each other…

or
https://nextcloud-talk.readthedocs.io/en/latest/TURN/