Google launched Discover performance reports in Google Search Console almost a year ago. It is available for sites that see traffic from Google Discover. So not everyone sees it.
But there is no API for it yet. John Mueller from Google said on Twitter “There’s no API for the Discovery performance data in Search Console at the moment, sorry.”
When will it come? Who knows. It does not seem like it is something anyone is working on right now but I can be wrong.
If you want to push Google on this, tell John why you want an API for this on Twitter:
Tell me more! What would this data in API form change (apart from “we want more data in API form”)? Thanks!
— ? John ? (@JohnMu) March 13, 2020
Forum discussion at Twitter.