Bluetooth tracker not working

Hi,
I am running Home Assistant 0.113.1 on py venv on a raspberry pi 4. I cannot make the bluetooth tracker work: no devices are ever found (not my iPhone, nor my tv, …).
I have installed an external bluetooth dongle but the problem still remains.

This is the configuration I have used:

device_tracker:
  - platform: bluetooth_tracker
    interval_seconds: 1
    track_new_devices: yes
    device_id: -1

This is the output of lsusb:


root@GC01hass:~# lsusb
Bus 002 Device 002: ID 174c:0825 ASMedia Technology Inc. 
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 004: ID 0658:0200 Sigma Designs, Inc. Aeotec Z-Stick Gen5 (ZW090) - UZB
Bus 001 Device 003: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Could someone give me some hints on solving the issue?

Thank you