install subtheme not working (unexpected end of json input)

I'm not able to reproduce this bug. I've tried using node 23.4.0 but it compiles without errors. I'm using DDEV and Aljibe (https://github.com/Metadrop/ddev-aljibe/), but anyway it should work the same with any environment as long as the Artisan release and node are similar.

Can you try using Aljibe and/or DDEV? To discard problems on your local setup.

Thanks for reporting, that error seems related to popper bootstrap 5.3 dependency ("for positioning dropdowns, poppers, and tooltips"), theme dependency is the same as suggested per bootstrap "^2.11.8": https://git.drupalcode.org/project/artisan/-/blob/1.x/artisan_starterkit...

https://getbootstrap.com/docs/5.3/getting-started/introduction/

<script src="https://cdn.jsdelivr.net/npm/@popperjs/core@2.11.8/dist/umd/popper.min.js" integrity="sha384-I7E8VVD/ismYTF4hNIPjVp/Zjvgyol6VFvRkX/vR+Vc4jQkC+hVqc2pM8ODewa9r" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/js/bootstrap.min.js" integrity="sha384-0pUGZvbkm6XF6gxjEnlmuGrJXVbNuzT9qBBavbLwCsOGabYfZo0T0to5eqruptLy" crossorigin="anonymous"></script>

Genrated "package-lock.json" expected generation for popperjs:

"node_modules/@popperjs/core": {
      "version": "2.11.8",
      "resolved": "https://registry.npmjs.org/@popperjs/core/-/core-2.11.8.tgz",
      "integrity": "sha512-P1st0aksCrn9sGZhp8GMYwBnQsbvAWsZAX44oXNNvLHGqAOcoVxmjZiohstwQ7SqKnbR47akdNi+uleWD8+g6A==",
      "dev": true,
      "license": "MIT",
      "funding": {
        "type": "opencollective",
        "url": "https://opencollective.com/popperjs"
      }
    },

When that happens you should be able to manage it manually, command is just a helper that will try to simplify process. So if that happens new theme folder should exists either way, but you will have to enable serialization module dependency & default theme manually.

As tunic said, i'm not able to reproduce this bug either, feel free to change status if you found new details to replicate.