> If I intend to use Matrix exclusively, do I still need to register on libera.chat, in order to participate in Fedora rooms?

I think if you want to show up on the IRC side with your expected IRC
nick (for example, for IRC meetings, for zodbot to recognise you, and
for IRC rooms that are set up to only allow registered users), then
you will need to register on libera.chat and then set up that account
with "@appservice:libera.chat" ("!username foo", "!storepass bar",
"!nick baz" should do the trick, and allow you to authenticate over
SASL - at least that worked for me).

This helped a lot, thanks.

I'd still prefer if I didn't have to register an IRC nick and didn't need to communicate with Appservice and NickServ (I just wish to forget about IRC completely), hopefully that will be possible in the future.