@Elucidating @tinker I would say it essentially is true. Everything you write on Twitter is readable by everyone the corporation allows or directs to read. That is already a lot of people, and you have no choice in the matter.
Mastodon is NOT a private platform either of course. Tooters should have minimal expectation of privacy. However their is a much greater measure of control in who sees your messages, plus it isn't driven by surveillance based marketing.