Mac trackpad double-clicking and letter keys not working

In addition to kaz-k's excellent advice, check your battery for swelling. Symptoms:

— Unexpected trackpad and/or keyboard behavior.

— The gap between the display and the deck is not even when the display is closed.

— The gap between the bottom plate and chassis is uneven in places.

— Some of the screws that hold the bottom plate have popped out.

— The trackpad surface is higher than the surrounding deck surface.

— The computer "rocks" a bit on a known flat surface.†

† — I find solid-surface and granite countertops very effective flat test surfaces.

If a Mac's trackpad is double-clicking unexpectedly and some letter keys aren't working, there are a few potential solutions. First, check for and adjust settings related to trackpad clicking and tracking speed. If issues persist, it could be a hardware problem, requiring service from Apple. 

Troubleshooting Steps:

1. 1. Check Trackpad Settings:

• • Go to System Settings (or System Preferences) > Trackpad. 
  • Adjust double-click speed and tracking speed. 
  • Ensure "Force Click and haptic feedback" is turned off if you're experiencing issues with double-clicking. 
  • Verify that "Use trackpad for dragging" is enabled if you're having trouble with dragging. 

1. 2. Keyboard Issues:

• • Restart: A simple restart can resolve temporary software glitches. 
  • Update macOS: Ensure your operating system is up to date, as updates often include bug fixes. 
  • Safe Mode: Start your Mac in safe mode to isolate the issue. If the problem disappears in safe mode, it may be due to a third-party application or extension. 
  • Reinstall macOS: If all else fails, reinstalling macOS may be necessary. 

1. 3. Hardware Checks:

• • Clean the Trackpad: Dust or debris can interfere with the trackpad.Carefully clean the trackpad surface. 
  • Check for Obstructions: Ensure nothing is stuck underneath the trackpad.  
  • Apple Diagnostics: Run Apple Diagnostics to check for hardware problems. 

1. 4. Advanced Troubleshooting:

• • Reset Trackpad: Resetting the trackpad settings to their defaults can be helpful. 
  • Check Mouse Settings: If you use a mouse, ensure its settings are not conflicting with the trackpad. 
  • Consider Service: If the problem persists after trying these steps, it may be a hardware issue, and you should contact Apple Support or an authorized service provider. 

Important Notes:

• If you're comfortable with more technical solutions, you can try resetting the trackpad properties files or uninstalling/updating third-party drivers. 
• If the issue is with a specific key not working, check if it's sticky or if there's any debris preventing it from pressing properly. 
• For older trackpads that don't have a USB connection, you may need to reset the Bluetooth connection.