I swear I saw yesterday this text 'This board/chip uses I2C 7-bit address 0x20' under 'Technical Details' left from the 6 pictures in the Adafruit-Shop. At the moment this information is missing. All is fine for me: it works now with LED as expected and also in series with button press, thx ScruffR.
I´m very happy and will document this as a project in the next days. It´s time to make an enclosure for this dome button.
Thx again, gentleman! Bye Core.