Mine is mounted with wiring channels so it would be a pain but I can tell you on channel 106 both the info banner and my SmartCast phone app both say HLG. The pop I expected is just not there. It is very detailed. Obviously 4K but I’m not sure how HLG differs from HDR.I have tested this using my Murideo 6A signal analyzer, and the DirecTV 4K box ( 61K ) is now outputting over 13Gb when playing 4K HLG 30Hz content. My LG C7 OLED recognizes the HLG signal and uses my chosen HDR10 picture mode. ( The DirecTV C61 signal looks great BTW ) Obviously that signal would require an HDMI 2.0 port which is HDMI 1 on the M70-D3. HDMI Ports 2-4 are HDMI 1.4 which mean they cannot handle a signal which exceeds 10.2 Gb.
My M70-D3 is in a different room and only has a DirecTV C41, and a Samsung K8500 Blu-ray. Obviously nothing I am playing back with that gear exceeds 10.2Gb, so any of the M70's HDMI 1.4 ports ( 2-4 ) will be more than adequate. Because my LG recognizes the HLG signal, it causes the C61 to crank up the data rates ( EDID ), but I haven't been able to test if this is the case with the M70, so I don't know if plugging in the C61 to the M70's HDMI 1 port would take full advantage of the C61's 4K/HLG output capability or not. The M70 might recognize the HLG signal as HDR10, in which case this would work - or it might not.
If that is the case, I would move the AppleTV 4K to HDMI ports 2-4, set its home screen output to 1080P/HDR/60, and turn on frame rate & dynamic range matching. Content playback from iTunes, Netflix, etc. will output around 9.2Gb ( 4K/HDR/DV/4:2:0 or 4:2:2 @24Hz ) so it doesn't matter if you are plugged into the only HDMI 2.0 spec'd port on the TV, as you do not need to be.
It's worth a try. If I could easily pull my M70 off the wall, and move it back to the family room, I could test this on my end and report back. I'm pretty certain that the M70-D3 will not recognize HLG, so its EDID will cause the C61 to output a 4K SDR signal - which will run just fine on any of the HDMI 2-4 ports.
I would love to know which is what! Would you be willing to mess with the above and let us know?