Neither Lemmy nor PieFed are able to follow Mastodon users, but Mastodon is able to follow/subscribe to Lemmy/PieFed communities, post to them and talk to their users. Following a busy Lemmy community from Mastodon will make the community flood a Mastodon user’s feed, though.

Mastodon can follow any Pixelfed account and vice versa, but Pixelfed will see only posts with photos and Mastodon will see no more than 4 photos per post. Pixelfed is able to post to a Lemmy community, but I did not try to follow a comm from there.

In fact, Mastodon is able to follow any account from any fediverse app, but all the content from this will be reduced to the lowest common denominator: a post, maybe with formatting.

and UpScrolled already having questionable ethics, this may be the path forward.

I am definitely Out of the loop on this.