How to join a #libera.chat #IRC channel via #matrix:

1. Type /join #channel:libera.chat into your client.

Done! 🤯

So #matrix isn't set up with #libera yet, but a kind soul on IRC reminded me that #biboumi exists, and tipped me off that disroot has one running.

I'll set that up instead of waiting for a matrix.org bridge, and I'll do an #HPREp on the steps required with Conversations and a SASL login to libera. It's going to involve using a second XMPP client that supports XEP-0050.