Flickering/Pixelated screen

Using an External Monitor - Reinstall the macOS

Use an external monitor. See if you can see the login screen. If so, reinstall the macOS. You would connect it a monitor or TV or projector with a HDMI Port. Perhaps a corrupted system file needs to be replaced - an a reinstall is intended to fix just that.

• Boot into Safe Mode:

Hold Down the Shift Key upon boot. Once at the login screen, release shift. See if it all now works. In Safe Mode, only necessary items load (i.e. the caches), and new preferences are set aside.

If nothing above works, then...

• Reinstall the macOS:

Nothing would be lost, it's just that sometimes changes are made to your system, and then then processes become corrupted, technically. When reinstalling, deleted files are reinstalled, and misplaced files are moved back to where they should be. Go Here: How to reinstall macOS from macOS Recovery - Apple Support.

Back up your Mac Prior to the Reinstall:

Are you Concerned of Losing Data?:

• If not, just move ahead and erase the disk and then install the macOS.
• If so, then first backup your macOS, using the methods I mentioned above.

Backing Up the Mac: Start by creating a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the reinstall. Go Here: Back up your Mac with Time Machine - Apple Support

afcadavid Said:

“Hey thanks again! Since I reinstalled the macOS and even erased the hard disk that should have erase all the errors in my user, but the issue is still happening. I did what you told me anyways, didn’t not work :(“

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Restoring from the Backup:

Did you backup the Mac at least (as I mentioned in my above reply)? If so, try restoring to it, as I mentioned above too.

Perform the Following the the Order Shown:

• Use an External Video Device:

Once restored, attach an external video device (monitor, TV, or Projector) using an adapter, if need be. If the error does not come up on the external video device, but it does on this Mac, then it is the Mac.

• Perform a Diagnostics Test:

So, before you go about restoring, perform a Diagnostics Test (Hold down “D” upon boot), and let it run. It will check hardware and other items. I would recommend you take a photo of the results shown on the screen, so that you can have a record of it for reference. Go Here: How to use Apple Diagnostics on your Mac - Apple Support

• Finally, Restore From the Backup:

Everything will go back to the way it was before the reinstall.

afcadavid Said:

”I tried all of them and none of them works, even after reinstalling the macOS it didn’t work, what’s weird it’s that when I go into safe mode the screen problem goes away! do you guys have any idea how to fix it?”

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User Account Management:

If it goes away in Safe Mode, then it’s probably some preference misconfigured in your current user. So, try creating a new Administrator User, seeing if this all goes away. If it goes away, then move everything over to the new user, and then trash this current user.

To create an Administrator User, go to System Preferences > Users & Groups > Unlock the lock > Click the “+” symbol > create an Administrator User.