We tried that. Did nothing but divide the community, cause increased cost, increased administrative burden, increased spammers and detracted efforts from actually working on the project. Ultimately, about five legitimate community members continued to used it over three to six months.
Matrix is IMHO a bad choice as it attracts the same demographic as Discord (glossy webclient) but is much more janky. Realistically speaking it is a poor Slack clone once you look beyond the technical aspect of federation which few people care deeply enough about to endure the buggy and half-broken user experience of Element.
I have had great success bridging to IRC (and XMPP). Yes, it will not fully replace Discord, but it allows a very dedicated group of people to participate in a community on their own terms and with great lightweight clients.
I agree though that any kind of bridge increases the risk of spam. But you should really try to get community members on board to deal with this kind of thing. Developing a software and running a community alone is not a good idea.
For you, I suggest sticking to Discord. I am of the mind that your effort should be focused on your community instead of enforcing a FOSS philosophy upon a group that may not have any interest in doing so.
If you are creating a new community, this is a different conversation, of course.