Yes, I did. Device /dev/ttyAMA0 is checked. There are no values in the optional configuration options. The addon is started and show a green button in the top right corner.
The Phoscon UI top right corner shows
Phoscon-GW172.30.33.5.
My raspbee II replace the Xiaomi GW and the Philips Hue, I am very pleased.
I beg the question though, why put a config.txt file in the root that cannot be reached by ssh or a samba share? I borrowed a PC to be able to reach the root directory.
On the SD card there is a mini partition that can be used under Windows and on which the config.txt is located. But only there the setting can be made. On the main partition is the Home Assistant which is a docker with limited access.