About sidecar files
Fotometis keeps a photo’s marks in two files, in the same folder as the photo.
Fotometis writes the rating and the flag to an .fmx file. Another app does not read an .fmx file, so the rating and the flag stay in Fotometis.
Fotometis writes the tags to an XMP file. Fotometis reads that file too, so a tag that another app wrote is a tag you see in Fotometis. For example, tag the photos in bulk with the Fotometis MCP server, then the same tags are available in Lightroom and other software. See Tag photos in bulk.
An XMP file is named for the frame, so a RAW file and a JPEG file of the same exposure share one.