Apple Keyboard

No known preceding event is troublesome 😟

Are you sure that there was no software updates or anything like that?

See if anything in these helps fix it

If your Apple wireless mouse, keyboard, or trackpad isn't working as expected - Apple Support

If your Apple keyboard doesn't work - Apple Support

My guess is that you inadvertently set a preference

from > macOS Sierra: If keys on your keyboard don’t work

...

If other keys don’t work

You may have accidentally set an option that changes how your keyboard operates.

• Choose Apple menu > System Preferences, click Accessibility, then click Keyboard. Make sure Slow Keys is turned off. If Slow Keys is on, you must hold down a key longer than usual before it’s recognized.
• Choose Apple menu > System Preferences, click Accessibility, then click Mouse & Trackpad. Make sure Mouse Keys is off. If Mouse Keys is on, pressing keys in the numeric keypad moves the pointer instead of entering numbers.
• Choose Apple menu > System Preferences, click Keyboard, then click Input Sources. Select “Show Input menu in menu bar.” Open the Input menu, then make sure the correct keyboard layout is selected.

  To see the keyboard layout, click Keyboard, then choose “Show keyboard and emoji viewers in menu bar.”

Sometimes the use of a keyboard extension USB cable can resolve connection

issues, or sometimes not. ~ Those connections in Mac's port or cable ends can

go funky; it's an idea, if you have an USB keyboard extension cable.

Also there are some articles about how to use non-Apple PC keyboards

(both microsoft and apple sides to the story) that may be useful if needed.

Links within: Re: Bluetooth connection problems - Mouse & Keyboard

You posted in the Powerbook (vintage notebook) forum. Do you have Powerbook?

What Mac do you have - model & year?

assuming that you have a desktop Mac, what keyboard do you have - year?

How to identify your Apple wireless mouse, keyboard, or trackpad - Apple Support

Have you changed the battery(s)?

Apple Wireless Keyboard, Mouse, and Trackpad: How to install batteries - Apple Support