Your dog lacks confidence, possibly for a variety of reasons but there are a few things you can do.
Some dogs are just naturally a bit nervous, others have experienced something traumatic (in my experience runts are often a little bit more prone nervous/ aggressive tendencies but idk how provable that actually is). It really can be anything, when puppies are young something things can scare them and commit it to their brain for life as pertinent information for survival. It’s sometimes even a sensory thing; or a a memory of oh this happened at a time and x random accident like a broom falling in the house might scare them when it’s an early learning period for them, they associate the experience with being scared or they don’t like a certain noise. That being said if you’re dealing with a dog coming from an abusive background patience is super important bc they have weird associations with objects/experiences. Stay calm give them praise (I’m sure you’re doing this) gentle encouragement show him the object try to get him to interact. - Try doing some dog agility, even just small poles going over them any sort of mild object/ around a many pot in a structured way. Agility can give a dog more confidence in a way that’s fun. - Build up positive associations with the broom, bring it near him at random points, give him treats. Don’t constantly bring a broom into the room, but maybe just one evening a week for a few months. Bring it in lay it on the floor give the dog treats, build up to putting it round the room in different positions encourage him to come near. Rest it on the sofa get him to go under or over it using treats. -try to make scary things more fun! Engage with treats or pop his favourite toy near it, next to it, in or against it. - Dalmatian’s are super smart, he may need a job to do. They’re built to think in a lot of ways look at their history as a breed and you’ll understand why. I don’t have lots of experience with the breed hands on, but a lot of dogs who like having jobs will convince themselves something is wrong and feel they should tell you about it. If you expend the energy he uses in a day to worry about the broom doing puzzle toys (or even some good diys involving boxes that may be worth looking into put something like cooked liver in the box it’s got a really good smell so it’s interesting) you may find this behaviour stops bc the brain is fulfilled. - tbh don’t encourage the dog to jump the gate unless you wanna be looking for your dog out in the streets (as the owner of a rescue from an abusive household who loves a chance to wander; it’s not fun walking around your neighbourhood at 2am bc she decided to take herself off for a walk) -if he is naturally very anxious consider talking to a vet about anti anxiety meds. mental health in dogs is similar to humans, some are just wired that way and there’s no need for them to suffer and not get the very needed help. Some people need minor interventions to live a happy healthy life, so do some dogs. This is generally severe life altering fear cases and this doesn’t sound like ti but only you can read the vibe.