I Have a Roku Ultra hooked up to a Denon Receiver which goes to an LG OLED TV.
If I set the Roku to 720p it works fine. If I set it to 1080p it flickers and eventually ends up on a black screen that sometimes flashes an image for less than a second. 4K won't work because the TV HDMI Ports will not support HDR.
If I hook the Roku up directly to the TV it works fine in 1080p. If I hook the Roku up to the receiver and then to a different TV (TCL 42") it works fine.
I've tried all kinds of HDMI cables, they all produce the same results.
Basically, the only problem is the Roku connected to the receiver connected to the LG. Only that combination causes the screen problems.