This question is especially for people who have joined in the last week. Have you used other fediverse platforms or is this your first time really using one? What do you think of it so far? Are you aware that you can comment on Lemmy posts with a Mastodon account?
I think this is what you are looking for: https://the-federation.info/platform/73
I don’t know if it is “all the instance”, but it is a good amount.
And you can see the communities by typing
<instance URL>/communities, like https://beehaw.org/communitiesNeat thanks!