Currently, underscores are the only allowed separator chars for tags, and hyphens are not allowed and thus prevent a hashtag to be recognized as such. For instance, #hello_world is recognized, can be searched for etc., while #hello-world doesn't work. Obsidian (which I've used for my markdown files) supports tags with hyphens, so my files have quite a bunch of hyphenated hashtags, and I guess, those of other users might as well.