Thanks, Shawn, for trying to help.
Here're the gritty details of my configuration:
Workstation Build number: 12.1.0 build-3272444
host OS version: Windows 7/64
guest OS version: Windows 10/64
the OS version of which running VNC client: Windows 7/64
System keyboard layout of your host: (en-US or other?) de-DE
System keyboard layout of your VM: (en-US or other?) de-DE
System keyboard layout of the VNC client system: (en-US or other?) de-DE
VNC client software and version: (realvnc or others?) realvnc VNC Viewer (unlicensed)
Browser and version you used to access github.com: (Chrome, FF, IE or others?) FF, 64 bit (latest)