Hi Manfred,
If this is the case then you need to change the wording of this in your Getting Started with Raspberry Pi: Raspberry Pi 4 Model B
★Mount the Build Environment folder of your PC to this new share directory. Please use the IP address of your PC and your login name on the PC. In order to get access to your shared directory, you need to insert your PC login password.
My login name on my PC (Gerard Faber) is different than my login name (gjfaber@) on my Microsoft account and neither of them worked it is only when I used C:\Users\gjfab name (gjfab) and the Microsoft password, not my computer pin number that it all worked for me.
Thank you,
Gerard Faber