Can Meta scrape the data off other apps like mastodon from federated communities? I don't exactly know how that works. I'm assuming mastodon and other not profit based apps don't track any data so how would meta joining the fediverse change it?

I think it's all but given that meta would have the largest number of users using its apps in the fediverse. Threads already has 2 million sign-ups in hours so it would be a miss to just defederate from it and lock down millions of users from interacting with meta users. Let's see how it goes.

Edit: 5 million sign-ups in 4 hours according to zuck