Back in the day when our community was switching from xmpp to discord, our solution was to write a bot on either end that relayed messages from one to the other. The xmpp bot got more and more naggy over time until eventually we put the xmpp side in read-only for everyone except the relay bot. It did a good enough job at building momentum to switch that the final holdouts came over when we went r/o.

You might consider building something similar if you want to make a genuine effort to switch to matrix or IRC. A relay bot solves the problem of the first people being punished by virtue of being first.