How to restore my keyboard to default settings?
The default behaviour in macOS since 2011 is to display a menu of accent characters when holding down keys on the keyboard.

If you don't like this behaviour, you can go into the Terminal and disable it:

defaults write -g ApplePressAndHoldEnabled -bool false



  Once you’ve executed the command, log out and log back in to your user account. When you log back in, the accented characters will be disabled. Pressing and holding down a key on your keyboard will only repeat it.


This tip originated from https://www.addictivetips.com/mac-os/disable-accented-characters-on-macos/