It doesn’t sound like it’s limited to libera.chat.
Thanks to the standard, open protocols that IRC is built on, chat.sr.ht users are able to participate in the established community of IRC networks like Libera Chat.
EDIT: They do, however, appear to recommend it.
The recommended network for SourceHut users is Libera Chat: https://libera.chat
It doesn’t sound like it’s limited to libera.chat.
EDIT: They do, however, appear to recommend it.