Hi Max,
PixInsight does not support Bayer raw FITS files directly. You can read them, of course, but they are not debayered automatically.
Fortunately, Sander Pool has written a DeBayer tool that works nicely. You'll find it under the ColorSpaces category in Process Explorer.
What mosaic Pattern RGGB ?
I have no idea, but it's easy: try them until you get good results (debayer and use STF to inspect debayered data). Luckily, there are only 4 choices
