This mailing list is mostly inactive; the last email that wasn't a largely irrelevant crosspost was in March, and the one before that was five years ago. It was created when the WMF set up a Multimedia team around 2013; that team was disbanded a few years later, and while even later there has been another Multimedia team, I don't think they used the list. Now there is once again no such team, and the occasional question about multimedia features will probably see more activity on commons-l or a more generic list like wikimedia-l.
Spammers still find the list, though, and the anti-spam features of Mailman aren't great. Maybe it's time to close it?