Can’t log into Mac due to symbols appearing instead of letters
Solution 1:
You can fix the keyboard without logging in using these methods:
If you have a guest account, you can log in there and change the keyboard there.
Boot into recovery mode (cmd + R) and you should be able to change the keyboard from there.
Safe boot by holding shift as your computer restarts, and it should reset the keyboard (probably? I'm not sure about this).