Keyboard

Is this an Apple KB?

Are you running any VPN, Anti-Virus, or Cleaning apps?

Start with this...

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes or more.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

dr.robertfrompalm desert Said:

"Keyboard: Certain letters will not type on the keyboard"

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Fixing Key Issues:

Reset the SMC and NVRAM:

(Applies to Intel-Only Macs): Sometimes changes(i.e. formats) are made to the system and then settings (i.e. for Keyboard) become manipulated, technically.  So, reset both on your Mac. Perhaps the keyboard's settings for it keys are mingled. It might take upto three tries to reset both. So, be certain you have the time to do so.

Use of an Adapter:

Try using an external keyboard. If you only have USB-C ports, yet the connector on the external keyboard is USB-A, then this is the adapter you need: USB-C to USB Adapter - Apple

dr.robertfrompalm desert wrote:

Certain letters will not type on the keyboard

if by chance you are talking about 789uiojkl, go to Accessibility preferences and turn OFF Mouse Keys. Hitting option 5 times may also do it.