Missing files for BigSur and Monterey

Hello CorpNewt and others,

while download and BuildmacOSInstallApp.command worked for Catalina, it does not work for BigSur and Monterey. The download itself finishes successfully, but using the BuildmacOSInstallApp.command comes up with this message:

#######################################################
 #              Missing Required Files                 #
#######################################################
That folder is missing the following required files:
BaseSystem.dmg, BaseSystem.chunklist, InstallESDDmg.pkg, AppleDiagnostics.dmg, AppleDiagnostics.chunklist

This is true, as these files are missing and are not downloaded at all.

Now I have many questions. ;-)

Are these files required at all? Where do I get them? Why they are not downloaded? How can I create a working "Install MacOS.app" for BigSur or Monterey from the files I have?

For BigSur these files were downloaded with a total size of 12.46 GB, so there must be something at least:

#######################################################
 #                 Downloaded 6 of 6                   #
#######################################################

Succeeded:
  MajorOSInfo.pkg
  UpdateBrain.zip
  InstallAssistant.pkg
  BuildManifest.plist
  Info.plist
  InstallInfo.plist

I also tried it on Windows, the result is the same.

Many thanks for your input.