That’s what he did at first. So I would put the harness on and plop him in the yard. Once he started associating the harness with getting to go outside, he was all for it. Now when he hears someone pick it up, he’ll run to the door and wait for it to get put on.

My cats also did the same thing lol I just gave up on it and let them be indoor cats. None of them were interested in exploring the outdoors

You have to accommodate them to it. Mine also just flopped down on the ground when I first put him in it, but now he goes on full walks with us. Baby steps :)