Scraping public data is entirely different from collecting your contact history, location history, web browsing traffic, decrypting WhatsApp traffic, etc. etc. and on and on.
Fediverse instances can also do most of this. They know your IP and email, and the stuff you reveal about yourself. You could de-anonymize many users with those 2 plus the info they share about themselves on here, with a bit of OSINT work. Any fediverse apps could also get access to contacts or other locally-stored info on your phone.
"But I wouldn't use that app." Well then you wouldn't be someone using Facebook either. People using Facebook would also be the people granting shady fediverse apps undue permissions.