I've seen a youtube video that does it with what looks like a cheap rice cooker.
I think that you need to experiment and test to see how long it will take to cook; every rice cooker will be different.
To cook tarhonya in a pressure cooker or an Instant Pot, follow these directions:
1 cup tarhonya
1.5 cups water
1-2 tablespoons cooking oil
A pinch of salt
(The recipe is easily scalable ...