I have the same issue on my QN90B (also the same soundbar).
My older Samsung TV (a 2014 model) shows Sonos Beam volume level on screen when I adjust the volume. However my new QN90B it does not.
Is this issue specific to Sonos Beam and new Samsung TVs, or does it also happen with other soundbars?
Either way, if anyone from Samsung is monitoring this community, please update the software on your modern TVs so that it displays Sonos Beam volume level on screen, like your older TVs do.