If this is a power struggle and you let him win this, he will rule the
house. So I have to disagree, if you know he is capable and is just
unwilling, set boundries. let him know he CAN choose to pee and poo, but
you CAN and WILL choose the punishment. He will soon realise he can get
more of what he wants if he cooperates.

but ignoring the issue of potty training, but continuing to change regular
diapers without a fuss, nothing interesting, nothing exciting, or whatever,
isn't letting him win, it's not that he wants to wear diapers, it's that he
doesn't want to do what the adult wants, which happens to be not wearing
diapers, the converse does not apply.

The advice from many respected sources when an older child refuses to potty
train is to ignore the issue - my expectation would be that after a while of
ignoring the issue he'd likely start doing it himself.

Anne