Defederating or suspending will prevent your instance from seeing the content of another instance. Blocking the IP addresses associated with the domain will prevent the other instance from seeing your content by normal means. Meta could spin up a secret instance to spy on the fediverse (and probably already does this) which is impossible to stop, but this act is a means of protest.
I think you can be reasonably sure that anything you put out in the fediverse is indexable by any large company. Google is already indexing Mastodon posts, for instance.
Defederating or suspending will prevent your instance from seeing the content of another instance. Blocking the IP addresses associated with the domain will prevent the other instance from seeing your content by normal means. Meta could spin up a secret instance to spy on the fediverse (and probably already does this) which is impossible to stop, but this act is a means of protest.
I think you can be reasonably sure that anything you put out in the fediverse is indexable by any large company. Google is already indexing Mastodon posts, for instance.