Hey @Colours ,
how strange! Can I ask how long have you been experiencing this? Is the same thing happening if you run the phone in Safe Mode? Using Safe Mode on a Samsung phone or tablet allows you to force the device to run the essential operating system, and disable most 3rd party applications. It's designed as a diagnostic tool to help solve issues with connectivity, battery life, apps, and more.
To do this Press and hold the Power button until you see Power Off, Restart, and Emergency. Press and hold the Power Off icon until it shows a Shield, tap the Shield and the device will restart in Safe Mode. Once done, monitor the phone to see if the same thing happens.
Have the same problem on my S20 5G. The screen flashes every 6 minutes as if a screenshot is being taken. If this happens while using the full screen apps (like navigation or whats app call), the app minimises. The message app (with an blank screen) can be seen in the app drawer. I noticed that this does not happen when mobile data/internet is off or when in safe mode. I updated the latest software update (as available on 17th Oct 2021) and the issue still persists. Changing the settings in the message app, to set appear on top = off, may prevent the screen flashing and opening message app, but this may only be one visible step of the "attack". Since this happens only when internet is available, I'm worried it may be related to some kind of malware and more activities may be happening in the background! Samsung needs to resolve this ASAP.
