When migrating video files in a library that contains a Video content type, you get the following message:
One or more video files were migrated into a library with a Video content type. Sharepoint might have converted these files to a video DocumentSet at the destination.
When you copy a video file to a document library with a Video content type in Normal mode, SharePoint will automatically convert the video file into a Video Set (a particular Document Set for videos).
You will experience the same behavior if you upload the video directly to SharePoint.
To avoid this issue, you can migrate your video files in Insane mode if your destination is in Microsoft 365 or migrate your videos to a library that does not contain the Video content type.