There are many things to ask to my manager (non-meeting days, remove non mandatory people from invites, open team discussion on the topic). I guess this is more of a culture thing at work where everyone is "expected" to show up. I see my boss' situation as even worst (although one might argue that that is his job, I see this as quite unhealthy no matter the role)

The opposite viewpoint is that you are being included in these meetings so that you can prevent bad decisions by management. What if you aren't in a meeting where it is decided that you should implement feature x because they imagine it to be low cost, not realising the complexity?

I wouldn't ask them the question you just asked them.

The point is to see if they already have a solution in mind, and (if you're a good manager) either do it, tell them why it can't or shouldn't be done [yet?], or tell them they can do it themselves.

First off, I would set the strict max 30 minutes time limit for each and every meeting. If it’s not enough to solve something: do a follow up next day but ask everyone to prepare properly. Or just move the discussion to emails.

2nd: be an ass as a moderator. Cut all the small talk, chit chat, warm ups, derailing, or ad hoc brainstorming (usually performed by two people while the rest of the attendees are slowly dying inside).