UAC Steuerungsdialog Win10

[TiGü]

Zitat:

When no file association has been set by the user, or when an app corrupts the UserChoice Registry key while setting associations, it causes file associations to be reset back to their Windows 10 defaults. The UserChoice key stores an encrypted hash which indicates that the association was set by the user and not by some malware. It is a part of the new protection mechanism which exists in the operating system since Windows 8.

Quelle: https://winaero.com/blog/prevent-win...-default-apps/

Zitat:

Microsoft decided in Windows 8 (probably for security reasons) that users should be able to set default programs only via the built in GUI. I.e. by design, you are not supposed to be able to set default handlers in a script or programmatically.

Quelle: https://stackoverflow.com/a/27004486

Schlußfolgerung: Du kannst ab Windows 8 und aufwärts nicht mehr so wie früher zu Windows XP und 7 Zeiten die Dateizuordnung programmatisch setzen.