Consent must be informed and specific under #GDPR. Any Fediverse server may use consent or legimate interest to display public Fediverse content on their server. However, it is not clear to me how consent for or legimate interest of #Facebook repurposing data for behavior analysis/ads could be justified.
Every home server can also decide their API terms of use that Facebook would need to respect. (Disclaimer: I'm not a lawyer)
onepict