This always seems to be such a controversial view here, but if you think a meeting is pointless and that you have nothing to gain from it or contribute to it, just don't go. We're all grown-ups at work, and are ultimately responsible for our own productivity. Be prepared to articulate exactly why you feel some other use of your time is more appropriate, in case someone asks, but nobody is holding a gun to your head t…
Here's the one simple trick they don't want you to know about: email the organizer, making sure to CC everyone, asking for the meeting's agenda.
a more congenial approach would be to provide your understanding of the agenda, perhaps as a question, and then asking if there's more or another alternative: "it sounds like we're going to collectively make a decision on [x]. is there anything else on the agenda for this meeting?" even better if you do this one-to-one and, if needed, suggest the meeting invite be updated accordingly.