Plex only available via Plex Relay & Remote Access always changing from green to red after a few sec

Plex Media Server Remote Access
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4

My bad… I must have misread VM as VPN (or I finally need glasses).

Did you already have a look at the related troubleshooting support article?

https://support.plex.tv/articles/200931138-troubleshooting-remote-access/

There’s also a guide with some more details on how to troubleshoot remote access issues…