Testing the Fediverse's interconnectivity between apps and protocols

One thing that would have been nice to know as a newbie on the Fediverse:

The word out there on the Fediverse make it seem as if all the different tools (Mastdn/P-tube/Lemmy/etc.) can interact with one another. But this is not the case, as some work both ways, whilst others only one way, or at all.

So made accounts & been testing for past few weeks:

a) Hubzilla
b) Friendica
c) Mastodon
d) Kbin
e) Lemmy
f) Iceshrimp
g) Bonfire
h) Peertube
i) Funkwhale
j) Pixelfed

And just out of curiosity:

a) Using Bridgyfed, to test interactivity between the AT (BlueSky) & AP protocols (Mastodon, etc.)
b) Meta's Threads for testing with Mastodon.
c) Starting to test Nostr with its peer-to-peer network.

TL;DR:

The fediverse holds a lot of promise, but it the ideal level of interconnectivity isn't there yet. (And yes, not all of them need to be able to connect and interact on the same level of details as with the others, as they are different tools.)