Okay, i've checked and all of my crafts (and hopefully all of yours) exist.
It's just fairly complicated to find them. Really sorry if your on MacOS, but I only have a (semi) solution for Windows users.
First, you will want to quit KSP 2 for safety. You don't have to, but I would recommend it.
So, go down to you Windows search bar and type in this: %appdata%
Click on Open Folder.
It will open a hidden folder in File Explorer.
Your path will say this:
[INSERT USERNAME] > AppData > Roaming
Click on "AppData"
Now, click on "Intercept Games"
Next, click on "Kerbal Space Program 2"
Then, "Saves"
Then, "Single Player"
Then, click on you campaign name, for example, "Autostrut Aerospace"
Then, click on "Workspaces".
Then, find the craft you're looking for within that folder. There should be three different versions of the craft, all with different file extensions.
Open the one with the ".json" extension.
Open it in Notepad.
Then, you can select the text, and copy it with "ctrl + C"
Reopen KSP 2, and enter the VAB.
Once in the VAB, you can paste the craft in with "ctrl + V"
There's your long lost craft! Enjoy!
(This will insert the entire workspace.)
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Thanks for trying my fix. I hope all works smoothly on your end.
Thanks!