How to extract the filename without the extension and write that to a tag using ExifTool?
Make sure you're using exiftool ver 12.22+ and change Filename to BaseName.
exiftool '-Comment<BaseName' winter.mp4
If you have to use an older version, you can use regex to remove the extension
exiftool '-Comment<${Filename;s/\.[^\.]+$//}' winter.mp4