I have Roku, Amazon fire, Android and Apple TV 4K.

Honestly they all more or less get the job done. The Apple has the best specs, a very smooth UI, no adds or intrusive data mining and integrates really well into the Apple ecosystem.

The blanking is momentary for a second or so when you switch from SDR to HDR content. From then on it should be stable. Is that what you are experiencing on the Roku? You mention rebooting so seem to be describing something more serious.