XIAO + Grove Shield + RTC DS1307 with Circuitpython

I am desperate to get a Grove DS1307 in combination with the XIAO and Grove Shield working.

What I am struggling with is getting the I2C working - scanning the I2C bus, does not find the RTC with this code.

Is there anything that needs to be added to activate the I2C / SCL/SDA on the XIAO/Grove Shield?