- pair and connect with the Android phone, remember to enable bluetooth tethering on Android
nmcli deviceshould have a new device with type:bt, copy the device name, i.e.AA:BB:CC:DD:EE:FFnmcli device connect AA:BB:CC:DD:EE:FF
in KDE Plasma, connection should show up on system tray
UPDATE on 2020/07/18:
no need to run
nmcli device connect AA:BB:CC:DD:EE:FF, connection will automatically show up on KDE system tray