Flickering screen on iPhone 13 Pro

We can determine whether this is a software or hardware issue by performing a Forced Restart. That will delete any corrupt software files and re-index the file system, so if this is a software issue, this should fix it.

• Press and quickly release the Volume Up Button
• Press and quickly release the Volume Down Button
• Press and hold the Side Button until you see the Apple Logo.

If that doesn't fix it, then this will prove to be a hardware issue, possibly a screen digitizer issue, in which you should make a reservation at your nearest Apple Store's Genius Bar or Apple Authorized Service Provider. They will run diagnostics on your iPhone and determine the issue, then present you with your service options.

Genius Bar Reservation and Apple Support Options - Apple

Hello!

Force restart the device: Force restart iPhone - Apple Support

If the issue occurs again, have the device checked out at a Genius Bar or Apple Authorized Service Provider (AASP):

• Genius Bar Reservations: Genius Bar Reservation and Apple Support Options
• Locate Apple Stores & AASP’s: Find a Reseller 
• iPhone Service & Repair: iPhone Repair and Service - Apple Support

Have a great day!

Just 1 or 2 quick blinks as the screen lights up after waking it?