Can an animal companion with 3 Intelligence — and therefore not limited in the choice of skills or feats — take Item Mastery feats in order to channel magic items using Fortitude?
I think you're seeking an answer on the PF1 Rules Forum; this if PF2's.
I miss my Highly intelligent animal companions from 1:e, they where power-houses.
Now they are just Meat pinjatas or mounts.
I think you're seeking an answer on the PF1 Rules Forum; this if PF2's.
I would agree, this looks like a PF1 question that has accidentally made it into the PF2 subforum.
In PF2 animal companions can't increase their int, doesn't get choices of skills, and doesn't get feats.
That said, assuming PF1 and animal companion with 3 intelligence or more...the companion in theory could take item mastery feats, but
They need to meet the requirements, which generally requires ranks of Use Magic Device. Which as a GM I'm not 100% sure I would let an animal take, even an unusually intelligent animal. And then beyond that you also have to have the fortitude (less of an issue). And then beyond that I would only allow the animal to be wearing/using magic items normally intended for mounts/animal companions of their type (I can't find the rules text on AoN but the slots an animal companion has available is dependent on body type). So they don't have access to all magic items. And I also don't allow for magic items to be "refit" so that they fit into a slot for that companion's body type. So you will be quite restricted in what items can be used, which would limit which item mastery feats would be available to them.
So....yes an animal companion could use it. But there are a lot of restrictions I would place on it.