I purchased Magix Video Deluxe 2021 this week and also the MPEG-4 FULL Codec Upgrade.
When I open a folder with video content the MOV and MP4 files don't have a preview and downloading them to the timeline is also showing anything. The older MPEG and AVI files are working fine.
I selected "MainConcept" by Program->Import/Export->Codecs. But this is not helping.