"Our cat eats potato."
No one says "papa". They say "papas." Saying "papa" is like using the singular of french fries.
It's rarely used in English either but it could be if you were meaning they eat all kinds of potatoes. Like I eat meat. Or I drink juice. But it's not so common.
Does anyone else think that this isn't phrased properly in English? I would never, ever say "I eat potato" or "she eats potato," even if it was describing a thing that I do habitually. I would say "I eat a potato" though. I suppose it doesn't really matter if the phrases to be translated are stilted English.
Same in Spanish... you would use plural for countable nouns or singular with article
Potatoes are potato, so the cat eats potato.
But either-or are okay, in my opinion.
it said that "the cat" is changed to "la gata" rather than "el gato" why they decided that, i have no idea
No, there is one cat, and it's 3rd person, so 'come' is alright. 'Comemos' would fit if the subject was 'we'