Our pup lives in a flat with us.

Potty training is fairly easy, but you need to have the patience, and it's not that difficult, even in a flat. Make sure that you give your dog enough exercise, both mental and physical. You may have issues with your pup barking when someone walks by your door, which you'll have to get rid of with training. If you work long hours, try to give your dog some exercise before you leave and make sure to have chew toys around. And if your puppy will need to go potty and you can't take them, have someone else take them outside. Crate training could be useful as well. Not much else to say, it's not as difficult as people say it is. If you have the time for a mal, it doesn't matter if you live in a flat or a house. Mals aren't for everyone, obviously, but if you train your dog well, give it enough exercise and take care of it, you'll have a happy lil (big) doggo. Good luck with your pupper and I hope I helped, even if a tiny bit :)