Hi MatoviyBob,
Thanks for using Apple Support Communities. It sounds like you’re having trouble with screen flickering periodically. I’m happy to help.
Since you mentioned that this began after updating, I suggest reinstalling iOS to see if the issue persists. While this shouldn’t remove any of your data, I suggest creating a backup beforehand:
How to back up your iPhone, iPad, and iPod touch - Apple Support
Then, you’ll want to follow the steps in the article below, under the section labeled “Put your device in recovery mode and set it up again”:
If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support
Should the issue persist after that, you’ll want to refer to this article:
Get help with the display on your iPhone, iPad, or iPod touch - Apple Support
Take care.