My puppy won't poop outside but will eat other dogs poop while walking..What should I do?

"He use to try to eat his own poop but I got him out of that."...... depends on what you did/said as he could have mistakenly associate the fuss you made with not toileting outside

Eating poo is known as coprophagia

Lots of pups eat poo as part of their normal experiencing the world around them, which is why when you start toilet training it is always done on a lead, that way you can just pull the pup away from it( without saying anything) and stop it....but eating of poo from  horse manure, cow pats, cat poo, fox poop and even other dogs' poo are common favourites.

It can be as simple as your pup needs more food than you are feeding. Bordom can play a part so mental stimulation is important, so as to give your pup more to think about

(Not common but)Depends on what the pup is fed lots of very poor quality food on the market which gives little  nutrition to the pup and means that poo tastes the same as the kibble you feed and because it is not getting the correct nutrition it is trying to fulfill that nutritional deficency.

Could be that you are feeding the correct food but for some reason the pups system is flushing out nutritents it needs, so again it is trying to eat poo to get those missing nutrients

Big thing is do not make a fuss as if you do you are instructing the pup that it gets lots of attention for doing it...so you can without knowing be encouraging the pup... so take away all/any poo, clean up always, teach simple things like 'watch me'... a treat held up and move it to your eye and say 'watch me' once the pup gives eye contact, let the pup sniff or lick the treat and repeat several times a day, so the pup learns  that 'watch me' means to look at you...so you can distract the pup if you see poo on the walk simply by saying 'watch me' and you pass ( of course the pup always needs to be on a lead) You also need to practice recall, which can be done daily ech time you feed your pup as recall for any pup or dog needs to be 100% before you trust your pup off lead outside, Another very important command is 'leave it' and leave it means leave ANYTHING be it a person, dog, cat, poo, treat, ball so a very useful command to teach and a quick tug on the lead  and 'leave it'

Of course a muzzle will stop it eating poo if you don't care to train your pup to stop, but it means you will have a poo covered muzzle to clean and the first time you forget to use the muzzle it will be right back to eating poo

You tell him "no" and pull him away.  I don't believe you housebroke a dog after he "pooped" outside your house once and you gave him a treat.

Teach him "no."  My dogs know "leave it."

"Why is my dog eating other dogs poop?" I just modified you question & put it up to google & here is a ton of information for you to dig through

https://www.google.com/search?q=why+is+my+dog+eati...

This is the last place to ask about it.

You should check with your vet and let him or her know what your dog is doing. Dogs often will do this as a way of populating their gut with healthy bacteria that helps them digest their food. Your dog sounds like he may need to be on a probiotic supplement, to help support his digestive function. Dogs and animals that are lacking in enough of a microbiome in their hind gut will instinctively try to populate that area, because they would starve if they didn't. That's why young foals (baby horses) will eat dirt, and sometimes, eat their mother's manure. They need the beneficial bacteria that they get from doing this, along with minerals like copper and zinc. The same is true for puppies and kittens.

The refusal to relieve himself outside is a training issue, not a health issue. You haven't allowed him to learn that outside is a good place to relieve himself, so he does it in the house.

It might help to put a muzzle on him when out BUT that would be a pity.   Fact is you need to be one step ahead re seeing what other bad owners have not PICKED UP and not let him off the lead so he can't get to it.   He could pick up any kind of infection doing the rounds locally, plus WORMS.

As for not emptying when out (which is another matter entirely) usually a dog will, with exercise, open his bowels.   So where IS he emptying?

Dogs in apartments are not easy unless you live on the ground floor with a private area from the apartment.  Getting housetraining accomplished is going to take a long time if you are floors up.   Something your dog's breeder should have warned you about!!

Dogs eat poop, it one of the many reasons to NOT let them lick your face etc...

You need to walk your puppy longer, ad realize he wont poop Every time you go outside.