Hello 
I took some time to test the new option (enabled at distance by DaveBinM). On my LG C1 directly connected to my ATV 4K 2023, I still had issues, until I disabled the bypass option ( Audio > Advanced Settings > Match Screen and Sound > Bypass ) that I had to enable before. Now it is much better, even though I still feel like I notice a small delay on 4K files (AC3, EAC3, DTS), for 1080p files, it seems to be in sync.
LG C1:
Bypass TV A/V sync OFF
HDMI audio bitstream ON
ATV:
Match framerate ON
Audio out AUTO
