Have you disabled any settings on your TV that might be compressing or changing the audio in any way?

Samsung Q9FN connected through hdmi arc port. 
Set to Dolby digital plus. Zero delay. No further settings selected/available. 

I just checked the built in YouTube audio is actually spot on with no delay. Although in the YouTube app, TV sound setting is in PCM instead of Dolby Digital Plus. 
 

I also tried the Netflix app in Apple TV 4K, no delay but Apple TV did do a audio sync setup. Apple TV only support Dolby Digital so it’s worse sound than Dolby digital plus in theory. 
 

So could it be a built in Netflix app issue? Is there any Sonos setting to set audio advance?

Play the audio before it’s actually arrived? No. Sonos can do many things, but time travel isn’t one of them I’m afraid.

What is HDMI Input Audio Format set to on your TV? Have you tried the other options? Is Auto Volume turned off?

YouTube videos will only play in stereo PCM.

There is no setting to advance the audio in the Sonos app.

It’s not a time travel if you can request TV a delay in video from Sonos?

That’s almost as tricky: Sonos doesn’t do video.

Some TVs erroneously delay the audio path for some codecs, esp for HDMI inputs. If the TV manufacturer wont fix it, the usual work-around is to switch to optical audio, as its a lot harder for TV manufacturers to mess that up.

I’m not asking Sonos to do Video. However, if a £800 product that is primarily designed for home theatre then Sonos cannot ignore the audio video out of sync issue. 
 

The Samsung soundbar can set audio delay in positive and negative timing. This suggested that the HDMI connection can set delay and advance timing with the TV already. 
 

There really isn't anything Sonos can do about this in practice. As @ratty has said, Sonos cannot play the audio any sooner than it is provided by the TV.  The only way to get sync is for the TV to ensure the audio output syncs with what is on the screen (or that the audio is in advance of the picture).

When the Samsung TV is used with a Samsung soundbar there probably is some proprietary, non-standard, HDMI-CEC communication that enables it to sync. An audio advance is of course really a video delay. Sonos can only make its HDMI-CEC conform to the standard.

Tne price of the Arc could be £8000 rather than £800  and there would still be nothing Sonos could do.