Strange danzing rectangles in blue line appear in the screen of every App

Each rectangle lasts 1 second an then moves position . The show lasts some 15-20 sec and then stops

Screen shots show rectangles line in red and the background in yellow while live the background is different and the line is blue

there is a case dated as of 2020 ans SE phone blaming the magnifier but here that is not the case

Any ideas on how to get rid of?