XMP files are a “sidecar” file that Mylio creates when changes have been made to your photos. Because Mylio is non-destructive, your originals will not be changed. Instead, changes will be recorded to the XMP file and the XMP file changes are applied to your original image.
XMP files are a standard for recording metadata for images and are used by many applications. Changes made in Mylio can be read by most applications that utilizes XMP files.
If you wish to apply metadata to the original (non-raw) image, you can do so with Mylio’s “Save Metadata to File” option.