Maximum screen resolution with AirPlay Extend Display on the Apple TV 4k?
I had some luck with my lg 65 inch 4k display.  By turning off underscanning in the Apple TVs Airplay menu I have gone from having bars around my 'external' display and this seems to have increased the clarity of text.

However, I am still faced with only scaled options for 1080p and 720 on my macs display options for Apple TV.

I guess there could be two reasons for this...

Requires a High Sierra Software update to enable 4K mirroring

The network bandwidth required for 4K streaming may be a challenge to ensure a smooth experience and hence why it is still not possible.

it would be nice to have the option either way....if it came with a disclaimer that performance may be delayed at least id have a choice to put up with it or not....