I can’t sign in bc the keyboard will not pair with the Mac.

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

1. Connect the USB keyboard and mouse to the computer.
2. Open System Preferences – Bluetooth
3. Un-pair the wireless keyboard and mouse.
4. Turn off Bluetooth
5. Restart the computer in Safe Mode per the directions in https://support.apple.com/en-us/HT201262
6. Restart the computer normally.
7. Open System Preferences – Bluetooth
8. Turn on Bluetooth
9. Re-Pair the wireless keyboard and mouse.

10.  Unplug the USB keyboard and mouse and begin testing the wireless devices again.

Hi,

check if the Bluetooth is ON. And try to pair again

1. Turn on the wireless keyboard.
2. Click the Apple logo at the top left corner of the screen and hit "System Preferences."
3. Click on the Bluetooth.
4. Put the keyboard into active pairing mode.
5. When the keyboard name appears re-pair it.

All the best

If you have a wireless Apple KB, using the charging cable to plug into a USB-A port will make it a wired KB. The times I've done that I connected via a port on the backside of the Mac. No idea if it it'll work connected to a hub/dock.

It the keyboard has rechargeable batteries connect it to the Mac with its charging cable and it'll work like a USB wired keyboard. Then try what the others have recommended.

If you can't log in, you will need to buy or borrow a keyboard from a neighbor to be able to sign in. Then go to System Preferences and see if you can pair your wireless keyboard.