By the sounds of things, your dog might be bored and/ or frustrated when left home alone.
And while that is certainly a much better starting point, this is still a separation related issue and needs to be addressed.
So what to do next:
Ensure your dog gets adequate physical exercise and mental engagement (adequate to age, breed, energy levels, etc).
If your dog gets overwhelmed with excitement every time you go to your front door, expecting to go out for a walk - work on desensitising them to the front door (look for the Door Is A Bore series on my Instagram) and let them know when it’s time to go for a walk vs when you are leaving on your own (check out my video on leaving cues).
If your dog has created a wonderfully stimulating job of barking out the window at passers-by, manage their access to the window and cover the view (I.e. frosting).
There are of course many more reasons why a dog might be bored or frustrated when home alone and if you feel you need help, please get in touch so we can discuss your dog’s specific situation and needs.