UPDATE Nov 15 with new video https://youtu.be/vw4ia4-OmHE
I hope this helps other LG C9 or CX owners get the most out of their Series X console.
Vincent with HDTVTEST did a great video on the subject here: https://youtu.be/5Y9qcXMQg_s
1. Make sure to change the icon in the dashboard to PC. This resolves issues with speckling and lines in some games.
2. Make sure to turn on ALLM and VRR support in console.
3. Turn on HDMI Ultra HD Deep Color and Instant Game Response for VRR to work properly. Optionally you can engage FreeSync Premium which does include LFC support.
4. Dolby Vision will be greyed out if you turn on FreeSync Premium because LG does not support FreeSync Premium and DV simultaneously (will become important soon once games support DV).
I would also like to add that there is a beta firmware that many have installed that fixes some flicker issues near 120Hz according to users on twitter. The raised blacks issue with VRR is not resolved in this upcoming patch and is inherent in the panel. LG has publicly stated that they are working on gamme curves to help with this in a future firmware update.