No it "belongs" (in your sense of the word) to the platform used to publish it. You loose a significant part of your rights to that content (be it public or private).

The only way to "own" your content is to publish it on your own domain on a host you just pay for storage. You might then link to the content via your (so called) social playground of choice. But you will own the content in a "normal" use of the word.

You can even explicitly state a copyright-info and lay out your terms, that tell everybody that this is your creation, your belonging...

Posting it publicly on any platform that you do not own, will end in you loosing rights to your creation.