I have a newfie who's just over 1 year old (I know, it's the raptor phase, but for the most part she's pretty well-behaved) and ever since she was ~6 months old, whenever she's outside she will endlessly bark at neighbors, walkers, or any of their animals if she sees them. Otherwise she's pretty much silent out there. She loves everybody and is trying to be friendly and get them to come play with her, but she doesn't understand that her big bark is threatening. I can handle dealing with her noises myself, but I know it must be bothersome for the neighbors and I don't want them to hate us. There are several other nearby dogs and they hardly ever bark, so she's definitely the problem child.
She doesn't do greeting barks when people come into the house or, for the most part, while on leash. Mostly that's just whining and flopping around trying to get their attention, but she's taken training and direction well for moments inside houses or while on leash. The problem is just when she's free in the backyard and sees what she thinks is a new friend.
Overall, unless she's scared or confused about a new object, or she's trying to get our attention for a good reason (needs to go to the bathroom, we forgot a meal, etc) she's quiet and will stop barking once the need/desire/concern is resolved, and we've done a pretty good job of never rewarding demand-barking so it doesn't happen anymore except for the occasional boundary test.
She also used to do a general-purpose set of barks as soon as she got out the door, but I've been able to discourage that by praising her silence in that moment and giving a verbal "no" and/or leaving immediately if she barks.
The problem is that once she gets locked onto another person or, especially, other dogs, all sanity leaves her and she enters monster mode. She refuses to acknowledge any commands (she absolutely knows come, sit, stay, etc and we can use those as interruptors for other types of unwanted behavior) and won't even look at me in most cases no matter what I do. Entering the backyard when this is happening either riles her barking up even more (as if I'm providing a safety barrier and she feels more bold or maybe thinking I'm giving her my approval), or just redirects her crazed energy towards me (sprinting at me, jumping, nipping, zoomies; anything she can think of to try and get me to roughhouse with her, which she loves).
She'll bark like this no matter how much play or exercise she's gotten. Her intensity level may be lower if she's been tired out, but the switch will always get flipped, especially if she sees another dog. Once she's in that mode she ignores all commands or treats – I can literally rub beef liver (her favorite treat by far) on her mouth, walk back and show her how it's right inside the door, and she'll just give me that sassy look before taking off in the opposite direction to go bark more rather than allow herself to be contained.
I know that part of this age range is hyperactivity, sassiness, destructiveness, etc and I can deal with all of that, but the barking is way too loud and way too long for the neighborhood. Short of tackling her to the ground and dragging her inside (which she loves and would consider a reward for the behavior), almost nothing interrupts it and she'll actively evade all attempts to stop it, redirect it, or get her inside where she'll settle down usually immediately.
For reference, she's overall very obedient aside from these moments – she will very consistently listen and obey in almost all other situations. She's a good dog! I just need her to stop causing so much noise outside.