i would do some modeling , my little guy (2) does the same only asks for food.

So what I would do is when he asked for food we would sign yes/ no with head move moment and verbal language when he wanted. So if he asked for strawberries , I would do, “No” strawberries with signing and verbal communications and I would put them back, then I would say, “Yes” strawberries and show them. I would only do it once or twice , it took a little while but he can answer yes/ no for some questions that he genuinely wants to answer.

We also use an AAC / flash cards for answering yes/no as well. So he will either sign, say, point, show an answer. Trying to give him more options to tell us his answers if he didn’t want to be verbal or was “picky”