bernd1-1@web.de:
What do you recommend to use instead if I'd like to replace my current BIOS? Should I install coreinfo and carry on with https://doc.coreboot.org/tutorial/part1.html? Should I use SeaBIOS and is there a tutorial for SeaBIOS, too?
Continuing with the tutorial link and choosing SeaBIOS will result in the most likely to work firmware. If you do a web search for "x220 coreboot" (without quotes and replacing x220 with your model if that's not it), you should find several step by step guides on how to go about it. The pictures they have are useful when performing the external flashing step towards the end.