Hi @Jakob_Schumacher - welcome to Discourse Meta 
If you are logged in as admin, you can basically add .json to any page - for example:
https://example-forum.org/admin/reports/daily_engaged_users.json
https://example-forum.org/admin/reports/page_view_total_reqs.json?end_date=2024-05-22&start_date=2024-04-22