I have a Roku Express 3700X. I have sound but no picture. Just a black screen when using Netflix, Disney Plus, etc. I’ve updated everything, restarted and even unplugged Roku. Can’t seem to figure it out.
I had that same problem and tried several things. I might suggest that you go to "system", click on "Display and see whether you show 720 or 1080. You will also have the option of "auto search". Try that first (after you have noted whether you are currently 720 or 1080). If it still comes back to the same setting, just manually switch to the other (720 or 1080). I have used this "trick" a couple of times on different units and it seems to work. It's worth a shot! Best of luck!