Skypack is definitely unmaintained, newer code breaks Skypack.

[trusktr]

F.e. https://cdn.skypack.dev/lume@0.3.0-alpha.27 currently forwards to https://cdn.skypack.dev/error/build:lume@v0.3.0-alpha.27-XyqUZ0QD4LxUz3lBtzzc, which shows the following error message, and I think it is because EcmasScript #private field syntax that even all browsers today support:

/*
 * [Package Error] "lume@v0.3.0-alpha.27" could not be built. 
 *
 *   [1/5] Verifying package is valid…
 *   [2/5] Installing dependencies from npm…
 *   [3/5] Building package using esinstall…
 *   Running esinstall...
 *   Failed to load node_modules/lume/dist/cameras/PerspectiveCamera.js
 *     Unexpected token (87:4) in lume/dist/cameras/PerspectiveCamera.js
 *   Install failed.
 *   Install failed.
 *
 * How to fix:
 *   - If you believe this to be an error in Skypack, file an issue here: https://github.com/skypackjs/skypack-cdn/issues
 *   - If you believe this to be an issue in the package, share this URL with the package authors to help them debug & fix.
 *   - Use https://skypack.dev/ to find a web-friendly alternative to find another package.
 */

console.warn("[Package Error] \"lume@v0.3.0-alpha.27\" could not be built. \n[1/5] Verifying package is valid…\n[2/5] Installing dependencies from npm…\n[3/5] Building package using esinstall…\nRunning esinstall...\nFailed to load node_modules/lume/dist/cameras/PerspectiveCamera.js\n  Unexpected token (87:4) in lume/dist/cameras/PerspectiveCamera.js\nInstall failed.\nInstall failed.");
throw new Error("[Package Error] \"lume@v0.3.0-alpha.27\" could not be built. ");
export default null;