To be true everything we post online can be used for training. Reddit is just made for money :P Kinda using more Lemmy now for posting and reddit just for browsing like archive.
As an PeerTube instance admin ( I self host mine) the global search need to be enabled by admin otherwise it will only search content of local instance though it only affects search not direct query or user channels URLs. Trending system usually is based on channels that are being subscribed by users of specific instance. about P2P it’s possible to disable it by admin instance to get direct connection without sharing.