i can't view the .mp4

what is flickering just the sign-in window or the whole desktop?

if you think mathematica is doing it then i think you should call support

however. did you uninstall the last version of mathematica before installing the new? do you ever get "lock ups" on your machine or flickering on any other app ? is your machine running win10 or Sierra (a pc or apple?). say it's a pc/win10 and you have a gaming card: issues with the gaming settings could cause a problem and furthermore if it's an nvidia type - the driver has settings on a per app basis (and a default for all apps). if those options are changed or wrong for mm, that could cause "flickering". but moreso: so could a bug caused by something else or by an OS that needs to be re-installed

but ask support if you think it's not really pc related