This was posted on Twitter by a person named Abhishek Yadav.
Android 11 Will Launch On September 8. pic.twitter.com/5C9prC7ynC
— Abhishek Yadav (@yabhishekhd) July 8, 2020
According to this, the official release date of Android 11 is September 8 .
In other words, if this information is correct, it means that this day is when the Android 11 update will start to be delivered to the Pixel series.
I’m not sure what the source is, but it looks like a notification that Google has issued to app developers.