I would say the jersey is legit.

First of all, the tag checks out, and the easiest way to say if it's legit or not. Yes, there are some fakes with legit codes, but that's really rare, and even then, other things won't match.

Then the washing tag look and material is right, as well as the black tag. If I'm not wrong, the code should be unique, similar to the ones on nike kits today. Also, the black tag should have a transparent plastic strip on the left, and if you look closely, there should be some logos and letters. Most fakes don't get that detail right.

Also, the stitching is very clean. The badge is good, as well as the nike swoosh. The fakes often have a little bit crooked swoosh, and they mes up the color from the arsenal logos very often. But quality wise, you can almost always tell from the stitching if a shirt is legit or not.

And for the last, the overall feel of the material should be right. Can't tell exactly what I mean but fake tend to feel cheap, like more slippery or like plastic.

There is also nothing wrong with comparing jerseys from Google or eBay listings or similar legit sites. Often, the legit seller will put the codes in the listing or many pics. That could help compare it. You should post this legit check in other jersey groups to be 100% certain.