We can use matrix client to access to #rpmfusion on Libera.Chat
First to simplify the process register you nickname on Libera.Chat
After login https://chat.fedoraproject.org choose start a new chat, write: @NickServ:libera.chat at @NickServ:libera.chat write: IDENTIFY <your_user_libera.chat> <your_password_libera.chat>
nickserver replies with "You are already logged in as <your_user_libera.chat>
and finally join to a public room: #rpmfusion:libera.chat
register user on libera.chat via matrix.org it is possible but confuse see here https://fedoramagazine.org/access-freenode-using-matrix-clients/