Weight Loss For Cats:

Weight loss in cats is EASY if you know three things.

1) Dry food with nothing on it or mixed in it.

2) Cats MUST eat every day. But they don't have to eat much.

3) Cats won't lose weight if they share a bowl because they'll get more or less than they should.

So. Choose a "less-active" or "low fat" cat diet.
A dry cat food.

You'll be feeding in teaspoons or tablespoons.
You can put down the tablespoons all at one time for grazing weight loss.
It's even better to put the tablespoons down twice a day and supervise it. They'll come running once they figure out that there's not food out "all the time"

Whichever way is easiest to avoid 'communal' food sharing.

This is how much you should feed your cat per day, divide it in half for 'twice a day feeds'.

If you want your cat to weight 9 pounds - give 18 teaspoons (level) ONCE per day.

Here's an EXPLAINER with a Chart of How Much to Feed a Heavy Cat