Potty training an extremely stubborn 3-year-old who refuses to sit?

I’m at a loss potty training my 3-year-old. He’s physically ready, just to cut it short I won't list all the signs. But absolutely refuses to sit on the potty or toilet. “Put him on every X minutes” simply isn’t possible, no matter what he doesn't want to sit on the potty or toilet and I can't physically force him, that tenses his sphincter even more. We’ve tried books, rewards, everything. We bought this frog-shaped urinal that was a novelty for 2 days but faded away quickly, now he says things like he wants to break and destroy the frog.

He also won’t tell us when he needs to pee.

This is our third attempt, with long breaks and zero potty pressure in between. I worked in daycare before and been around lots of toddlers, I have nieces and nephews and little cousins, so it's not new for me how 3 year olds are but this kid is stubborn on another level. Most kids at his daycare are diaper-free now, so I’d really like to make this work. Any tips specifically for kids who completely refuse the potty/toilet?