Both .meps and .mepx files are projects from Movavi software, with the key difference being that the first comes from Slideshow Maker and the later from Video Editor.
There is some kind of interoperability available in Movavi software, which means it is possible to import / reuse some content, but it's unlikely this works as direct file conversion.
If you for some reason need to export these projects or their parts and struggle with it, it might be best to reach out either to Movavi support or perhaps to the online community for further assistance.
Updated: January 2, 2024