Perfect way of putting it: https://pluralistic.net/2022/12/23/semipermeable-membranes/

Because Mastodon is free software, and because it is built on an open standard, anyone can add this feature to their Mastodon instance. You can do this yourself, or you can hire someone else to do it for you.

What’s more, if Mastodon’s core devs decide to take away a feature you like, you and your friends can stand up your own Mastodon server that retains that feature. This is harder than using someone else’s server – but it’s way, way easier than convincing Twitter it was wrong to take away the thing you loved.