The Bluetooth Manager in Linux Mint 22.3 detects the Logitech K380 keyboard, but doesn’t display the pairing code, or doesn’t display it for long enough (supposedly 10 seconds, but I didn’t see it at all).

There are two approaches:

1. The script from ValeriaRoyal/logitech-k380-bluetooth-linux-fix is the simplest version. Scans for the code and gives you 60 seconds to enter it.
   I didn’t try this one, but if I were to do it again it would be my first option.

2. From this StackExchange answer – using bluetoothctl, which comes installed on Linux Mint.

For the latter, the steps are:

$ bluetoothctl
Agent registered

[some prompt]# agent on
Agent is already registered

[some prompt]# scan on
Discovery started
....

Pay attention in the output for the input-keyboard line and get its MAC address. Then turn the scan off and pair the device:

[some prompt]# scan off
Discovery stopped
[some prompt]# trust <mac address>
...
[some prompt]# pair <mac address>
pair <mac address>
Attempting to pair with <mac address>
[CHG] Device <mac address> Connected: yes
[Keyboard K380]# [agent] Passkey: 987123

Enter the passkey it displays on your keyboard and it should be working!