Question: Can I upload a YouTube short from my personal computer?
As long as you have a video file less than 60 seconds long and of appropriate (i.e. vertical phone or 9:16) aspect ratio on your computer, then you can upload it to YouTube as a short by simply going through the normal upload process. YouTube will then recognize it as a short from the time and aspect ratio.
You can also put “#shorts” in the description, although this is not strictly necessary anymore as the YouTube algorithm is now smart enough to identify shorts without the hashtag.