I voted Instagram, but it's really not by a wide margin...
Be very careful with reddit, as the culture over there frowns on self-promotion. You can get away with it on subreddits where your content is directly related to the theme of the group, but read over the rules of the group before you do. The YT self promotion themed subreddits (and there are a bunch of them) are just link dumps. No one is browsing to find stuff to watch. Even the ones that require you to review and comment on other vids get empty reviews and comments and trigger poor retention analytics.
Facebook is even worse with link-dump groups.
You can add Tictok to the "other" list, but basically you will have to edit together an alternate version of your vid with a verticle aspect ratio that's under 1 minute long. And if you aren't doing a funny dance or adding a voice to your pet vid, don't expect a lot of views.
And then there are other video sites like BitChute, Vimeo, and LBRY... You may be able to expand brand awareness beyond YouTube without re-uploading your entire catalog. It's at least a good idea to claim your name on these other sites.