mix to bmp conversion is most likely related a graphics export, considering the BMP output format in the query. When it comes to .mix files, several different formats exist, but the most likely conversion for this is old .mx files from a tool called Microsoft PhotoDraw. You can still find graphics editors or converters that support this MIX format, so these are your only viable option if you are looking for a way to export these files to BMP format.
Updated: September 28, 2023