In case you're just having trouble using just the 1 network, here is the instructions for trying to connect to Libera.chathttps://libera.chat/guides/connect
The Tor instructions are further down on the page, and hopefully they give you enough clues to figure out what your problem is, and then you can post to the forum once you figure out how to do it right
They only have 1 server that lets Tor connect, and because of abuse they require you use a mirc-options/connect/options/SSL client certificate, which means you need to first connect there to register a nickserv account, and then be connected in order to attach the certificate's fingerprint to your nickserv account, which are 2 things you can't do from a Tor connection, which means you're leaving a record of the true IP address which 1st connected using that certificate, though I guess maybe you could do that from a friend's house or from a fastfood wifi hotspot.
Well, I guess you don't have to actually be connected using the client certificate in order to add its fingerprint to your nickserv account, as long as you're logged into nickserv, so you could login at someone's house and copypaste the certificate fingerprint hash there, without actually bringing the certificate there.
I reported that to Libera as a security hole, but they don't consider it a problem, though they seem to be the only network I've yet encountered which does not require you to use a certificate to connect to them while adding that fingerprint to nickserv.
If you're concerned about having some networks that you connect via TOR while other networks you don't use Tor, mIRC now allows you to have a per-network client certificate so you're not needing to use the same fingerprint from a Tor and non-Tor connection. Though you would probably want to have mIRC installed into 2 different folders, 1 for Tor and 1 for not-Tor, and not login to the same nickserv account from both.