The old BIOS version had been 1.49 (3rd July 2019). I scheduled the BIOS update (on Ubuntu) with 'fwupmgrupdate update' to version 1.54 at first (wich is not the latest version). After that I have downloaded the zip archive for 1.55 (1st November 2019) from https://support.lenovo.com/us/en/downloads/ds539061. The next step is a Tumbleweed installation.