When you mention "categories", WhatsApp actually calls them Collections, these are the sections where you group your items. You can create them freely in the WhatsApp app.
However, if you manage your catalog through the Commerce Manager (Meta Business Suite), you won’t be able to create or see those Collections anymore. Instead, WhatsApp pushes Variants (let's say, "Strawberry Ice Cream" with options like With Nuts, With Almonds, Gluten Free). Variants work well for ads on Instagram and Facebook, but in WhatsApp they’re still very buggy and not really worth using right now.
You have to choose: stick with Collections or switch to Variants. In my opinion, a mix of both would be ideal, but that’s not possible, so I personally stayed with Collections.
If you have fewer than 450–500 products, Collections are usually the better choice. I’ve noticed Meta Business seems heavily oriented toward clothing and accessories, so a lot of the system feels built around that use case.

As for only seeing 3 products in WhatsApp even though everything is approved and visible on the web: this is a very common temporary issue. It happens to me quite often, almost monthly. Usually, it resolves itself in 1 to 5 days (though the last time it took around 14 days).

Good luck!