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Have you tried this?
Reset the PRAM or the NVRAM on Your MacBook
A flickering screen can be a sign of a corrupted MacBook. Resetting the PRAM or NVRAM of your MacBook can restore its default hardware settings. Doing this also sets up the internal hard drive as the startup disk.
In order to fix your MacBook’s flickering screen, you can reset the PRAM/NVRAM as a possible solution as well.
Follow these given steps to rest the PRAM or NVRAM on your MacBook:
Shut down your MacBook using the Apple Menu. Make sure that it is completely shut down and not in reset mode.
Press on the start button again and wait for it to switch on. Quickly, start pressing the following keys for 20 seconds Option + Command + P+ R. Make sure that you are holding it down for 20 seconds without interruptions.
This will make your MacBook restart with the PRAM or NVRAM reset and fix your flickering screen.
Reset the SMC of Your MacBook Pro
You can reset your MacBook’s SMC to restore the default settings that you cannot modify via System Preferences. Sometimes, SMC-related issues can affect your MacBook performance and also create bugs. If none of the above solutions are working, you can give resetting SMC a final try.
Under SMC are the thermal management, power button response, sleep settings, battery management, lighting settings, and so on. Resetting the SMC of your MacBook to default settings can prove to be of great use.
Follow the given steps to reset the SMC of your MacBook:
Press on the power off button on your MacBook. After doing so, simultaneously hold the given keys for 10 seconds straight. Shift + Control + Option + Power key.
When the option tray appears, press on Reset the SMC of your MacBook to Defaults.
Release the keys after ten seconds. Your SMC Is now set at Default.
https://www.technewstoday.com/macbook-pro-screen-flickering/