This is when things get satisfying! My boss was included on the email to my team, and he called me about half an hour later asking about it. I hadn’t told him much about the Lizzy situation, because he has very little patience for people complaining about their interpersonal conflicts to their boss, and while this is a lot more significant than an interpersonal conflict, I thought he wouldn’t want to hear about it anyway, especially since he doesn’t have much contact with my team in normal times and has had even less while we’ve been virtual.

This is a situation where if this person's manager wasn't such a slacker, and refused to do his job, it would never have been an issue.

OP literally wrote to a third-party advice column seeking help before they escalated to their own manager because he's such a terrible leader. That kind of leader needs to be fired.