Bird and other animal food is of lower quality than what the government mandates be served to humans. This means that even though birds are smaller and can be more easily affected by things like fungal Aspergillosis, the manufacturers aren’t legally obligated to use the same quality standards they do with humans. In the wild, birds drink water from puddles and watering holes where animals poop and pee in the muddy water so its not really that great of a concern. However, if you don’t have the immune system to deal with those conditions then you succumb to them. Similar to Montezuma’s revenge if you visit Mexico or the poor that live in the slums of India. Their immune system can handle it but an outsider can’t.
Most of the time, established pet food companies generally are pretty good at keeping their products wholesome but money still talks and they too have bottom lines. Just being honest. So I would recommend that if you’re going to get nuts, feed them human grade nuts. My birds are so so with pecans and walnuts but they like peanuts and LOVE almonds. Birds are picky eaters so they won’t eat whole almonds but they love almond slivers. Whole almonds are rather large for them to fit in their beak so you can crush them up too but its just as easy and cost effective to get the slivers. Kaytee makes the Kaytee Fiest Papaya Peanut & Mango treat which is good. They also make Oat Groats which are great.
But whatever you feed them make sure it doesn’t have any added salt, sugar or additives. The ingredients shoud be the product and that’s pretty much it. Dried fruit will almost always have a preservative, usually Sulphur Dioxide which as far as I know is OK but make sure they don’t have any additives.