With the Zuckerberg takeover impending, there's a lot of confusion circulating about the use of user-level and instance-level blocks, and how our online expressions can be secured against Meta. Everyone who objects to their accounts being mined by the Zuckerberg entity for data collection, AI ingestion, monetization, and possible ghost-profile building needs to understand this problem. Here's information to clarify.
Neither a user-level block, or an instance-level block, will protect our posts from Meta data-mining by default on a Mastodon instance. Posts won't be delivered directly, but can be ingested by other means; if, for example, users on Meta-federated instances boost them.
However, both user and instance blocks will totally prevent post delivery in all cases IF your host instance has enabled the functionality called Authorized Fetch.
By default, Authorized Fetch is off on Mastodon instances and most haven't turned it on. If this concern is important to you, you might want to respectfully reach out to your admins and let them know. Remember that they are working hard to provide and sustain online community at no charge. It's likely they won't be very familiar with it and will need time to look into it.
