Don’t touch the raw crop. It has nothing to do with IBIS. What does have is lens correction. I haven’t found any exif tag for Canon and IBIS movement.
The black frame to the left and above is normally used to generate the correct black level Measure black and white levels?
How the white level for R6 CR3 was done for RawTherapee Canon R6 CR3 support · Issue #5901 · Beep6581/RawTherapee · GitHub
Your raw file seems similar to the JPEG in RawTherapee, without any DCP.
