https://github.com/yt-dlp/yt-dlp/blob/master/supportedsites.md

Reddit is listed in the list of supported sites. I just tested it with a random post video post on Reddit, and it downloaded the file perfectly fine (played in local player). My theory you either did a user error and gave a link that is not a video post, I'm not sure if posts that link to a video would work, I think the post itself must be a video post. Or you tested it when Reddit blocked yt-dlp. The yt-dlp team needs to update it first, then it functions again. YouTube does the same.