Hello Andrew McCall,
The saved image should reflect the crop, so this appears to be an issue with the integrated Designer editor rather than expected behavior.
For now, use the local Photos editor:
- Open the image in Photos.
- Select Edit image or press Ctrl + E.
- Select Crop, make the adjustment, then save the image.
This uses the built-in Photos editor instead of the online Designer experience and should provide a practical workaround.
If local cropping works, please report the Designer behavior through Feedback Hub.