I've made the mistake many times of freezing Xcode by opening a large JSON file in the editor - unfortuntely re-launching Xcode often doesn't help, as Xcode will attempt to open the file again every time you launch the application.
To prevent the editor from opening again, you can delete the Xcode Autosave Information directory (assuming you've saved all your files correctly).
cd ~/Library/Autosave\ Information ls -la #Inspect contents before deleting rm -rf ~/Library/Autosave\ Information
And now you should should be able to open Xcode again. 🚀 I hope this saves someone a few minutes 😅