In a recent email to users of anyone with a Google Analytic property, Google announced the final days of Universal Analytics are almost here. Even though the official deadline to migrate UA to GA4 was on July 1st, many people expressed their surprise on Twitter when the property was working many days past the deadline
Although now it seems like we have some clarification from Google – In about 10 days, the Universal Analytics Property on Google Analytics will no longer process any more clicks.

In the email, Google offered additional support for validating and linking your old properties to the new GA-4 property. They said "In about 10 days, your associated Universal Analytics property will stop processing hits. To get started, you can follow these steps to validate your new Google Analytics 4 Property."
So 40 days past the deadline is the official sunset date of Universal Analytics. RIP. You will be missed.