snippet.sh

sudo xcode-select -s /Applications/Xcode.app
xcrun /Applications/Xcode.app/Contents/Developer/usr/bin/safari-web-extension-converter /path/to/extension

manifest.json need to be version 2. Version 3 will cause error.

Then refer to this article: https://bartsolutions.github.io/2020/11/20/safari-extension/

Open the X-Code project of your Safari extension. Press “run” button. It should auto run your unpacked extension in Safari

If extension reports error: Failed to load resource: The requested URL was not found on this server. contribution.js:17. It's not enough by just adding new file to the folder. You need to manually add file to your project directly in X-Code.