Some Bluetooth devices block connections by default, or require you to change a setting to allow connections to be made. Make sure that your device is set up to allow connections.

Your Bluetooth adapter/dongle may not have been recognized by the computer. This could be because drivers for the adapter aren't installed. Some Bluetooth adapters aren't supported on Linux, so you may not be able to get the right drivers for them. In this case, you will probably have to get a different Bluetooth adapter.

Make sure that your Bluetooth adapter is switched on. Click the Bluetooth icon in the menu bar and check that it's not disabled.

Check that Bluetooth is turned on on the device you're trying to connect to. For example, if you're trying to connect to a phone, make sure that it's not in airplane mode.

Many computers do not have Bluetooth adapters. You can buy an adapter if you want to use Bluetooth.