Yes, they can harm your plants. Mostly, they’ll just make the leaves look eaten and ratty, but won’t kill the plants outright.
You can knock them off your plants into a pan of soapy water. You can also spray the plants they like with insecticidal soap with NEEM oil in it. It won’t kill them, but they don’t seem to like it, and will move on rather than stay and feed on plants that are sprayed.
You could also place bait bags far from your desired plants. Though there is some discussion whether those don’t actually attract even MORE beetles into your yard than would be there anyway.
When I had an organic garden, I would add composted kelp to the soil, which seemed to discourage any number of pests.
Japanese bean beetles would take one bite of my beans, and then fly away to eat my neighbors garden. :o)
