i think it’s functionally impossible to know every comment on every post in every community on every instance. but you could probably get about 80% of it. i have some 60+ fediverse identities across various services and i found that mastodon is incredible at getting lemmy content: if you subscribe to a community, every comment will be pushed to your home feed. in reverse chronological order. and mod deletions don’t get federated to mastodon.