Any investigation would require to know what hardware, if any, is between your phone and your monitor.
Aren’t you showing us the Built-in display though in that screen shot? Can you use the pull down menu to change to the secondary display or is there no secondary display available in the menu?
I think that might be a known problem (limitation, at this stage).
Regardless, on any Linux computer that I have used, a working HDMI connection at best adds a sound output device and you can choose whether sound will output via HDMI or via a number of other existing choices. (For example, even though HDMI is always capable of carrying audio, the actual video output device may not have any means of outputting audio e.g. no built-in speakers and/or e.g. no attached speakers.)
my TV is recognized/identified with proper name, resolution and refresh rate.
HDMI sound came with an update from about 4 weeks ago, i guess.
As long as the TV is recognized properly i can select HDMI as sound sink in Settings/Sound.
but, from time to time when i plugin the TV into the HDMI port of the hub it does not work.
TV stays black, no desktop; Settings identifies the TV as unknown/unknown with wrong resolution(one my TV can not render) and refresh rate.
in this situation i re-plug the hub, re-plug hdmi and/or reboot the phone.
if all of this does not work i re-flash phone!
I guess it is defaulting to VGA resolution. I am a little surprised that the TV can’t handle VGA (which is supposed to be the emergency fallback when higher resolutions don’t work) but then a TV is not designed to be a computer monitor (and to be fair VGA is now embarrassingly old).
There are a couple of packages around that allow you to debug EDID to see whether there is some confusion with that happening, but I don’t know whether those packages work via a dock.
It may also be a good idea to check the system log for the time at which you plugged in the TV.
I would probably replug the TV into the HDMI connector of the hub in the first instance if things aren’t working. Reflashing the phone seems a bit extreme and not a really viable ongoing solution.