Issue configuring ZHA

I’m using HASS for about a year now. I have it installed on HASS Blue with a ConBee II stick. Sofar I’ve connected all my devices via MQTT. But there is a specific light that keeps giving problems (switching on by itself, flashing, etc) and I try to eliminate the causes. Therefore I would like to test it without MQTT.

So, if I install ZHA via the automatic or the manual config flow, at the ‘Serial port setting’ it cannot connect to the dongle. I seem not to be able to install ZHA, reboot the system and try to connect.

Any suggestions on how to debug this issue further?