Canon EOS R5: Long Exposures and Image Stabilization are a Destructive Combination
When are camera manufacturers going to stop being clueless?
Leaving image stabilization enabled for longer exposures can cause wholesale destruction of image sharpness.
This is not unique to Canon mirrorless; I’ve seen similar problems with Sony.
Canon EOS R5: Destruction of Image Sharpness by Image Stabilization
Includes a comparison with/without image stabilization.
Below, image without image stabilization.