Question: Is there a tool I can use to generate theme.json?
Answer: There used to be one for an earlier structure of experimental-theme.json.
The tool, at gutenberg-theme.xyz is now a bit out of date. There are outstanding requests to update it.
Until the tool has been updated it makes sense to copy and cobble theme.json from a theme that has been updated to use "version": 1.
Reference
In the long term, if you’re going to develop your own theme or child theme, then it makes sense to understand the structure of theme.json and how to change it to satisfy your needs.
