Observe the percentage of people with their camera on (vs. some baseline), look at the faces you can see, watch for reaction emojis, take intermediate points to solicit questions and see how many you get, etc.

I often just honestly ask: "does it make sense, what I just said"? Often people are that "yes" but sometimes I get questions like "but doesn't X already do this, what is the difference?" etc that are very useful.

I find one thing that sort-of works for me is to stop often and prompt questions from the audience.

Repeated dead silence means (to me) that no-one is interested.