Flickering screen on MacBook Pro
How to stop a flickering screen on a MacBook Pro
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What is the exact model/year of your Mac?
If it is a 13" MBP 2016, check if it is eligible for this service program 13-inch MacBook Pro Display Backlight Service Program - Apple Support
If not, you can try these steps
How to reset the SMC of your Mac - Apple Support
Reset NVRAM or PRAM on your Mac - Apple Support
Restart holding D to enter Apple Diagnostics and tells us the outcome.
Well, based on the symptoms you told us, I'd say this is a hardware problem, maybe flat cable.
Take it to an Apple Store or Authorized service provider for it to be checked properly.