API: how to get joined at date in user summary

Hi everyone.
For the company I work in, we are extracting data for some groups of users and statistics for each of those users. The endpoint "https://{organization_url}/u/{username}/summary.json" shows the statistics we need but doesn’t show any date.

On the other hand the endpoint "https://{organization_url}/g/{group}/members.json", allows to get all users in the group and certain dates such as added_at, last_seen_at etc. For some users the minimum added_at date matches the joined at date that is shown in the user summary (see attached image) but as other members could join discourse under no group or joined first to a group that we are not interested in, so we cannot get that piece of information.

Is there any way to get the joined at date for each user using the current API?

Screen Shot 2022-05-11 at 15.41.48

Thank you in advance!

Used the Data Explorer Plugin and access the query from the API (there is a topic about that too)