You’re always free to spin up your own server and host it if you’re concerned about the way your data is being handled. Not something you can do with the corporate alternatives
And only post on your own instance and talk with users of your own instance… Might as well just send emails to your friends at that point…
But as soon as you interact with literally anyone (or anyone interacts with you) your data is still replicated on other servers.
Your posts are all public and discoverable by web crawlers even if your instance didn’t federate at all. That’s kind of the point of activityPUB
No personally identifiable information or private account information is transmitted between instances. The only thing that is synced is the content of your posts, reports and up- and downvotes. And all of that serves a purpose and is shared willingly.