Go back to basics - raw or dried food from animals smaller than the cat.
My cat, Zippy, will not eat anything but plain dry food. He won't eat any gourmet snack from a pouch or top of the line wet food in a can. I've tried most of them.
Dried chicken jerky is easy to produce and dried anchovy type fish so cheap as not worth the time to dry yourself.
@FrayedBear . I've tried many different approaches, including several kinds of human foods. Nothing but dry food attracts Zippy. He does like the more expensive dry food like Iams.
@OldGoat43 what is "lams"?
Well if he ever deserts & goes feral the wild life needn't worry - he'll soon starve to death. Not.
@FrayedBear . Not to worry. He refuses to leave the house. When I leave the door open to pick up my deliveries or mail, he stops at the threshold and never takes a step over it. He knows which side of his bread is buttered.