As far as I’m aware, Friendica does this. One feed, lemmy posts, mastodon toots, and Pixelfed posts all there. Lemmy is trickier because you can’t follow people and depending on the way you look at it, comments can show up as individual posts.

This is awesome, thank you. I switched from memmy (iOS only) to voyager because it doesn’t display code blocks properly (usually doesn’t even show what’s in them) so reading certain posts or comments about computers or programming was a disaster.