Yes, I don't get HDCP errors with FRM off. (According to the folks in the Roku section of AVS Forum, FRM is a well-known cause of HDCP errors with the Roku.)
Today I plugged the Roku directly into the TV instead of going through the Denon AVR. I had FRM on. Watched a Dolby Vision program for several minutes and got no HDCP errors. I had the TV sound going back into the AVR via the eARC port. Apparently there's some interaction with the Roku going through the AVR that's causing the HDCP errors with FRM on. So it appears that if I want FRM on my Roku (4802), I need to plug it directly into the TV instead of the AVR. I can live with that.
"I don't get HDCP errors with FRM off."
Well, that statement of mine was proved false last night. I started an HDR program on Hulu and got HDCP errors a couple times within the first 5 minutes. I was going through the AVR. Today I watched the Notre Dame game on Peacock for probably 1 1/2 to 2 hours. The game was in HDR, I was going thru the AVR and I got no HDCP errors. The inconsistency is maddening. It appears that the only solution is to use the LG native apps or run the Roku directly into the TV and get sound to the AVR via the eARC port.
I get the error at either sub-sampling setting, i.e., 4.2.0 or 4.2.2.
The only way I can use FRM without getting HDCP errors is to run the Roku directly into my TV bypassing the AVR. I use the eARC port on the TV to get audio (DD or Dolby Atmos or whatever the streaming program has) back to the AVR.