This would provide the ‘tasks completed’ attribute currently offered by the Todoist integration.
Google Tasks API: https://developers.google.com/tasks/
FWIW, this was previously a rather “unloved” product/service/offering from Google: extremely poor UI, desktop only, few (if any) integrations. However, it seems Google has doubled-down on Google Tasks: alongside the new Gmail update, Google Tasks got a brand new app for iOS/Android, a completely revamped Gmail integration, and a lot more. This update includes new developer docs: https://developers.google.com/tasks/
Seems like Google is investing more into this product. Since Google Tasks is very prominently featured in the new Gmail update, I would bet their user numbers increase a bit. Hopefully, along with new users, comes new votes for this integration :)