You can cook anything in an air fryer, as they don't actually fry.
There are two types, what I call the 'bucket' ones, like the Ninja Foodi variety, and the 'mini oven' ones, like the Tower. I have one of each - a Ninja at home and a Tower at our lodge. I am cooking a home made pie in the Tower one now. I made the pie as usual, and am baking it in the 'fryer', which is basically a mini convection oven. Because it is small, it heats up almost instantly and takes far less time to cook things than a big oven.
Anything that will cook in an oven will cook in it. I have baked, made Yorkshire puds, casseroles, roast potatoes, rice pudding - all sorts of things. As it has shelves, you can cook a few different things at once, but you have to rotate them as the ones on top cook faster than the things on the bottom. I've made a (small) Sunday dinner in mine, just to see if I could. The peas ended up being done in a bowl in the microwave, but otherwise I did a roast, yorkshires, roast potatoes and parsnips and an Eve's pudding in it, and it was lovely.
I like the Ninja less, as the pot is not suitable for putting on the table, yet is too small to fit in a casserole dish, so if you wanted to make, say, a cottage pie, you would have to do it directly in the pot and plate it up before serving. Also, getting things in and out of it is a faff, and it is easy to burn yourself. Stacking foods so you can have eg chicken and chips cooked together means that you need racks, which are fiddly and tend to tip over. OTOH, the Ninja has lots of functions, so if you don't have an electric pressure cooker and/or a slow cooker, it does those things as well. It also does things most people probably don't need often, such as make yoghurt and dehydrates fruit and meat. If you want to do those things, it's the gadget for you .
Personally, and people will disagree, if I had got the Tower first I wouldn't have one for the Ninja, I'd have got another one of those, BUT I also have an Instant Pot which pressure cooks, and a slow cooker, and that makes a difference.