Hello Gianmarco,
Can you share the dataset?
1. Metashape will undistort images, trying to correct them will result in worse results
2. Don't touch the original images, because by creating a panorama EXIF information will screw-up
3. To calibrate the lens you need a checkboard at the same focus-distance of your pictures, and the same camera/lens of course
4. Try to add some manual marker in metashape to help the alignment (pro version only), but don't do anything with Photoshop, DxO, or any other software. Changing the geometry / metadata will create issues.
5. Stick to the default settings for now