Does the HDR optimizer not work in HDR mode? Do you manually have to change to SDR2020 for it to become available?
Otherwise I wonder why you're not running with HDR on and doing the HDR optimizer on top of the regular signal that's stored on disc?
HDR optimizer can be turned on in HDR2020 or SDR2020. I just personally think the picture looks much better if you use SDR2020 and let the player do all the tone mapping.
IMO the player's tone mapping is better than the 885's built in HDR TM, so I keep it on SDR2020. Personal preference. You can try it both ways and see which you TM method you prefer. If one was using a custom curve than it might be a different story.
To me, the blacks are better, colors pop more, and highlights are better when I run SDR2020 and let the player do all the TM.
I think of the UB820 as a poor mans Lumagen. Looks great. I only wish it had an HDMI input like the oppo so I could use the TM for my apple 4k tv