- You should use pageview.
- You should use app installs.
- You should use purchase.
- You should use lead.
The Correct Answer is: You should use lead.
Explanation: As a marketer looking to track product newsletter sign-ups on your website, you should use ‘Lead’ as the conversion action. ‘Lead’ captures specific customer actions that are valuable to your business, like newsletter sign-ups. Tracking these conversions provides insights into how your ads drive these valuable actions.
Read more here: https://support.google.com/google-ads/answer/6032150