Aranet Integration fails - solved

I’m running HA on a Raspberry 4. Software is up to date.

I got an Aranet 4 CO2-meter and would like to install the Aranet integration.

When I try to load the Aranet integration, HA instantly says: “No unconfigured Aranet devices found”

The Aranet integration depends on Bluetooth. I have installled the Bluetooth integration and it has found the build-in device bcm43438-bt. Unfortunately I don’t know how to confirm that the HA-BT is working. ChatGPT suggests the command “sudo systemctl status bluetooth” but the command is not recognized.

The Aranet 4 is within 1 Meter from the Raspi 4 running my HA, so it should be in the BT range.
And “Smart Home Integration” is enabled in the Aranet App.

Any idea what might be wrong or what I could test? Thanks …

Update:
I brought the Aranet device even closer to the Raspi (30 cm) and all of a sudden the integration succeeded. Obviously the range of the build-in Blutooth is pretty short due to the metal case I put the Raspi in.

Update 2: Even with the Aluminum case removed, the Bluetooth range of the Raspi 4 is only about 4 m, with case less than 1 m.
I solved this problem now with an ESP32 based Bluetooth Proxy. Setup is fast and easy. Simon42 explains it well in this (German) Youtube video:
(4) Bluetooth Reichweite erhöhen mit Bluetooth Proxy in Home Assistant 🛜 - YouTube