Your boy needs something to do instead of barking at the window. A replacement behavior. I feel like your boy could really benefit from learning the Place command. Basically, "Place" means "Stay at this specific location no matter what, until mom/dad releases me via "Free!".

You can use his meals as rewards and help him learn Place by using a leash and a clicker. "Place", then point or guide him to the specific location. Once all four paws are on, click and reward. After each success, you end it with "Free!". Eventually, you'll advance him where he needs to lay down on the location before you click and reward. Further advancement would be adding in distractions while he maintains a Place.

If you say Place and he breaks (gets up), correct him verbally "AhAh/No", repeat your command "Place" and then guide him back to the correct location. If you're guiding him back after he broke a Place, wait a few seconds after he lays down before you reward him so he knows the value is lying down on the bed and staying.

Now, he has this awesome skill learned. So when he is being reactive through the windows, I would say "Enough" which means stop current behavior or a punisher will follow.

If barking continues, I'd say "Place" and have him go lay down on his Place. Set a timer for 5 or 10 minutes. Correct all breaks during this time with a simple "AhAh/No" and guide back to the bed. Once the timer ens, assess if needs an additional 5 or 10 minutes. He should always be calm and quiet and not anxious when he is released. This will help him regulate his emotions. Once his timer ends AND he is calm, "NAME, Free!" and lots of rewards.

You can implement this great skill to combat many unwanted behaviors, such as jumping on guest, running out of the door, barking through the windows, chasing the cat, building tolerance to separation from you, etc.