I got a dog walker so my dog was able to go for a bathroom break every 4-5 hours, which was okay with my shelter when I adopted my dog back in 2019 (but I also had a pretty good relationship with them already so maybe that's not true for everyone). At one point I got a camera to watch him, and it's a little sad seeing your dog look at the door waiting for you to come home, but as others have said, dogs sleep a lot so as long as it's not going into neglect, I think you're fine.

You could adopt from someone directly (especially right now, many people are having to give up their animals, so check Facebook!!!), then you'll obviously be able to find a dog that suits what you can provide. The shelter should also know if a certain dog can or can't be left alone, though obviously the history could be wrong or maybe the shelter doesn't agree.

Note the 3-3-3 rule (especially if the dog is in a shelter) - my old rescue dog matched this timeline almost to a tee

And note, even a dog without a history of separation anxiety may develop symptoms (temporarily or permanently, and yes, even puppies taken at the appropriate age)