Cache.mxc3 files with picture folder

Here there,

when I upload pictures, a file named “cache.mxc3” appears in the same dir.
Am I right in assuming, that that’s the cache for the thumbnails?

Thank you for answerng that stupid question!

Afaik, the mentioned file has nothing to do with Nextcloud or the thumbnails. It seems that the files are created/used by a software called " Magix Photo Manager".