From MSFS SDK 2020
The -mirroring parameter, in this version of MSFS sdk 2024 is always enabled by default.
In the documentation it indicates as optional.
Personally, I am interested in this being optional. Since in my AssetGroup folder I cannot have more than one .xml at a time and therefore when I compile it deletes the previous .bgl in the \Output folder.
Regards
Gio’