Hi there @anilerkan - welcome back to the community 
I had a peek there, and it looks like the Google Tasks API doesn’t have native webhook support. To avoid creating duplicates, you’d need to create some kind of mapping (such as name) and you’d have to create some polling logic like in as described here.
Here’s a quick workflow showing you the idea of what you’d need to do:
Just as a heads up as well, we’ve sunset the desktop app, and it will no longer receive the latest updates to n8n. You may want to switch over to either a cloud or self-hosted plan 