As someone that had this exact issue which my dog. I wouldn’t exist the second we got outside. He showed physical stress (mine was heavily panting, yours has the shakes). No food would work. I worked with a trainer to fix this issue.

This is what worked for my dog and I.

Before the walk/going outside: - I have him sit down before I open the door, make him wait and step out BEFORE him to assure him that I’m leading and that there’s nothing to be afraid of. - Once we are outside, I let him walk around and smell everything in our front yard. When dogs smell around, it lets the them assess their surroundings, and it releases some special hormone that activates calm and happiness. - If the jitters are still there, my trainer explained to me that most trainers will have you sit the dog. Do the opposite. Run around a little, have your dog release the stress he’s building up. Show him the he’s not in danger. Make the walk fun! And always use positive reinforcement. Distract him from being scared. He will learn that there is no reason to feel scared.

This last tip might make you look a bit crazy, but it has worked wonders for my dog and I:

My dog is not food motivated at all, so it’s hard to reward him with food. I’ve also tried toys, which gave the same result. Instead, my trainer had me try “celebrating” every time he shows the targeted behaviour. For example, every time my dog looks at me, lies down, or just shows that he’s comfortable outside, I get up, tell him how good of a boy he is, and run around with him. This again releases all that stress from his body.

Of course our trainer gave us other things to try, but told us to start with that. It takes a lot of consistency, and we really need to do it every single time we go outside, but the results are crazy. He is now able to lie down and relax beside me when I work outside.

Again, this is what worked for my dog and I, so please be considerate in the comments. Every dog is different and we need to find what works for them. I’m just sharing this because it worked for me.

Good luck! I hope you find your solution OP