A puppy learning to be on their own is all part of their training. This is NORMAL.
Sleep deprivation is used as torture for a reason, and just like children sleeping through the night, it gets easier, and puppies are faster!
Separation distress is different to separation anxiety.
It is important to create a Safe Space or “Zen Den”
Crate/Bed/Kennel
Create a safe and comfortable area for the puppy and make it look, smell, and feel inviting. Use soft blankets to cover the crate to make it darker then train the puppy to enjoy being in his safe space/crate. Never use this space as a “time out” or for any negative consequences.
Here are some tips.
The video quality is not great, but this is a perfect example of teaching a pup to enjoying being in a pen (restricted space) by Emily Larlham.
How to train your dog to be left alone- clicker training
This game can help with separation distress.
Yoyo game
You may need to crate (with the door open), tether, fence or have someone hold the lead to keep the dog in one spot initially. If someone holds the lead, no attention from them.
Wait for the dog to settle, lie down, or sit in a relaxed position. Don't give any cues—saying "Wait there, I'll be back in a minute" or "Stay," for example—as we want the ready behaviour to be a default and not something that needs to be cued.
With these small successes, you'll soon run out of room and will have to go through a doorway and out of sight. In keeping with a "set the dog up for success" policy, don't leave the room just yet. Take the dog to another room and repeat the procedure—from the start—in that room. Do this in several rooms in the house and then perform the exercise outdoors.
When you get up to 20 to 25 steps away from the dog outside go back to the first room and try going out of sight. When you are trying out of sight count seconds not steps. Starting again with 1 second and building up.
There is no food as the dog’s reinforcement is you returning to them while they stay calm. If they get up or become restless, we start again at one step. Remember to have breaks for playing and watch for signs of the dogs finding the “game” too much.
More Separation Training Tips
https://dogmantics.com/separation-training-tips/