One of the signs that your cat is losing its fear of the big bad world is when it begins to defecated outdoors. For the first couple months, most cats won't dare do their business outside. And then one day, when you least expect it, your cat will start sniffing and pawing around. Stop. Let it. And you'll find that after a minute or two, it will begin to dig.
This is a time to celebrate. Your cat has turned a small, but significant, corner. It is now secure enough in its surroundings to take a vulnerable stance and do its business. The first time, and maybe even the second, will likely be an emergency situation: it just can't physically hold it in any longer. But this will open the floodgates, and your cat will regularly begin to do its business outdoors. In fact, the activity of walking seems to bring it on.
And that's where poo bags come in. Buy them. You'll need to carry one from now on. You might, like me, invest in one of those little holders that you can attach to your cat's leash, so you won't forget it.
Yeah, it kinda sucks to carry around a little bag of poo until you can dispose of it. It's one of the things that dog owners do routinely, but we've been saved the indignity. Until now. And I have to admit, picking up my cat's poop, rather than being an annoyance, reminds me every time how far we've come. It brings the next corner in view.