Not sure if this changed recently, but the "Install macOS Big Sur.app" for 11.6.1 doesn't have a "InstallInfo.plist" at ...
/Contents/SharedSupport/. It only has SharedSupport.dmg in /Contents/SharedSupport/ and nothing else.
Also, doesn't look like that dmg has the info needed there.
Not sure if this changed recently, but the "Install macOS Big Sur.app" for 11.6.1 doesn't have a "InstallInfo.plist" at ... /Contents/SharedSupport/. It only has SharedSupport.dmg in /Contents/SharedSupport/ and nothing else.
Also, doesn't look like that dmg has the info needed there.
Maybe I'm missing something though.