Figured it out! Nowhere is this documented in Gugal or SearXNG docs, but the way to do it is to add the json
format to your search
config like so:
search:
formats:
- html
- json
This does make sense in hindsight as you are essentially enabling requests over the a JSON API however it is odd that this isn't documented anywhere. Also, note that if your instance is publicly exposed this makes it easy for bots to spam/scrape it.