Hi @SummerBummers We have a 4 month old Cockapoo and although she is a Velcro puppy, we don't have any problems leaving her for up to an hour when we go out. I thought if I let you know what we do, there may be something you haven't tried.
We have a dog crate in our lounge and it has a blanket over it. When she gets bitey or zooms round, we put her in the crate for quiet time but we are always in her eyeline as we watch tv or something. So, by doing this regularly through the day she has learnt to associate her crate with the place to be calm and sleep.
When we are going to leave her to go out, we start the process about 10 mins early. We out her in her crate, give her a dog biscuit and tell her to lie down. I put the radio on. Then, we get ready to go with her seeing and hearing us putting our shoes on etc, with us just keep repeating to lie down if she has a little cry.
I do think a big part of her being so good is that we stuck with the routine and didn't try lots of different things. She also sleeps 10.30-7.00 every night in her crate so is used to not having that human comfort overnight.
I really hope you can crack it and you can be less anxious leaving her. I'm sure you'll get there. I did prewarn my neighbours that if they hear her crying, it's just that I'm training her and they put my mind at ease and told me not to worry.
Good luck.