The Google Search Console Performance report API does not include Google Discover data. We've known that for a while. But the question is why? John Mueller of Google said the reason is "partially because there's no notion of "query"."
In March 2020, John Mueller asked for you, the SEO community, to let him know why you would want Google Discover data in the API. So it is probably something that is on the mind of some Googlers. But March 2020 through now has felt really long, really long ago.
Rob asked about it again:
@searchliaison Quick question - How do we pull Discover traffic into Data Studio (or elsewhere) via the Search Console API? Possible? I feel like it would be a 5th value here. pic.twitter.com/GcVhYyGcrC
— Rob P (@MrRobzilla) August 2, 2021
John explained:
The Search Console API currently doesn't include Discover data, sorry (it's not a part of the normal performance report API data, partially because there's no notion of "query").
— 🍌 John 🍌 (@JohnMu) August 2, 2021
I do wonder if one day they will add this data to the API, I do suspect so?
Forum discussion at Twitter.