TizenTube not running in 2k/4k, although TV has the resolution

[T3Cabon]

I noticed using Stats for nerds, that TizenTube is using a Viewframe of 1920x1080p, instead of 1920x1080*2.0 or *1.4.
I tried forcing the app resolution to 4k, but the app still starts in 1080p. Will there be a workaround for this?

Methods i tried:

TizenTube/config.xml:

• feature changed to: http://tizen.org/feature/screen.size.large (there are no spezified large res like normal.1080.1920)
• tizen:settings append screen-resolution="3840x2160"

TizenTube/index.html:

• head meta tag "viewport" added: <meta name="viewport" content="width=3840, height=2160, initial-scale=1.0, minimum-scale=1.0, user-scalable=no" />

All combinations of them

PS: I looked for the youtube.com/tv link with 4k enabled. They want a subscription for that?
https://support.google.com/youtubetv/answer/10383365?hl=en&co=GENIE.Platform%3DAndroid
But I found this browser ext, maybe it can be used to form TizenTube?
https://chromewebstore.google.com/detail/youtube-for-tv-4k/pdpkefmdjkgijhnhjkblpielhiikadbb