I still don't know how to switch to the JSON-only view the few times that I need it.
And I hate that quite a few extensions have a vague "just set X in settings" in their README's where X doesn't show up in the auto generated UI, and is called something else in JSON
Like tredre3 said there's also a button on the top right corner of settings, but I tend to prefer to start directly into json mode through the command palette.
Being able to find any sort of action with the palette just by typing is hands down the best UI design I've experienced in software. It's not new, Unity had it in the older Ubuntu distributions, but it's unfortunately not seen often enough and Ubuntu lost it when they moved to Gnome.
The palette search box also has the smart design of placing to the top functions you use the most through the palette, so if you open the json settings a few times it'll pop up at the top before you even finish typing the word "settings".
After a while, your interactions with the palette make its UI feel very personalized to your needs.
And I hate that quite a few extensions have a vague "just set X in settings" in their README's where X doesn't show up in the auto generated UI, and is called something else in JSON