I resolved a ghosting/flicker issue by changing "Dolby Vision" from always on to off.
Adjusting HDR subsample and auto refresh rate did not help.
Roku Ultra 4802X running 12.5.0 build 4178-C2 connected to an LG B7A 4K TV. Changing ports and cables did not help.
I believe the workload of converting all non Dolby Vision content (including home screen) is too much for the device and causes flickering and ghosting as well as audio drop outs. The TV would display frequent "Dolby Vision" indicators during use as the signal sync was reestablished. Playing the same content through native smart tv apps isolated the issue to the Roku, and changing ports and cables isolated it to a setting - forcing Dolby Vision for all content (default on OOB for my latest Roku).
