QNAP HS 251 HDMI output with Plex

Hi.

I am new here and maybe I did not choose the right category.
I do have a question for my QNAP HS 251, but I cannot choose the category above.

My problem:
On my QNAP HS 251 Plex Media server and Plex Home Theatre are running. I have a Plex Pass.
On my smartphone (Android) the Plex App (version 6.15.2.4143) is running as well.
The app receives data from the NAS, which is fine.

But how can I send videos from the NAS directly to my TV via HDMI using the Plex app on my smartphone?

The symbol on top of the app says: “Cannot find any devices”

The QMusic app of QNAP can both: Receiving and sending via HDMI output.

But how can I do it with Plex?

Thanks for your help.

Peter