Hi everybody.

I was unable to connect Logitech G603 mouse with GUI tool of KDE, but succeeded with bluetoothctl console tool.

I don't know what additional info is needed to debug this.
So if you tell me what to execute in console and copy-paste output here i would do it.

Thanks in advance.

Regards,
Daniil.

Sometimes, some Bluetooth devices don't easily connect via any GUI (not just Plasma). One option that sometimes helps is to try installing Blueman, and use that to pair the mouse.