Consider exempting Matrix.org users from OFTC registered nick requirement
The Matrix.org relay is the most straightforward way to access OFTC over Tor. Users who are accessing OFTC via the Matrix.org relay are not considered by OFTC to be "registered" by default, since their registration is with Matrix.org infrastructure rather than OFTC infrastructure. This produces a problem because Tor's OFTC channels are configured to disallow any user from joining if they are not registered on OFTC infrastructure. (I tested #tor-dev; I assume the others are similar.)
Usually, this kind of policy is intended to mitigate spam attacks. However, historically none of the spam attacks against IRC networks have been routed via Matrix.org infrastructure. This may be because Matrix.org has its own rate-limiting mechanisms for account registration (e.g. a reCAPTCHA test for each new registration), and it may also be because Matrix.org is new enough that spammers haven't paid attention to it. In any event, I think it's highly unlikely that you'll see spam from Matrix.org infrastructure if you permit Matrix.org users to access your OFTC channels.
Documentation on exempting Matrix.org users from the registered nick requirement is at https://github.com/matrix-org/matrix-appservice-irc/wiki/End-user-FAQ#user-content-i-am-a-chanop-and-have-a-spam-problem-how-can-i-fix-it-without-affecting-matrix-users . Any chance you could do this?
PS: I'm not sure if Community is the right component for this ticket; feel free to reassign to another component if you like.