I solved this one for my situation, hope the following notes help.
I noticed that my web version of plex would stream Tidal content when I was at work using Chrome or Edge, but still didn’t work from my home computer (on which the Plex server is running).
I found a Plex support article, and I checked my Chrome “content” settings because of this quote:
Note : If you disable DRM support in your browser, you may receive a security warning and/or be unable to play TIDAL content.
Still no luck. Then Then I found this forum thread, which gave me the final clue.
“Your connection to app.plex.tv has to be in https to be able to stream tidal content.”
Final solution:
I had my home Plex web browser pointed to 127.x.x.x:xxxxx/web/index.html, which looked normal, but could not play Tidal content. After I changed the web address to https://app.plex.tv/desktop, Tidal content now works!
