My Apple Watch Series 3 (42mm Space Black Stainless Steel Case With Space Black Milanese Loop) is approaching its end of life soon as it passes the four-year mark. I expected Apple to discontinue the Apple Watch Series 3 this year (2021), but it lives to die another year.
If you are on the non-cellular Apple Watch Series 3, you will run into problems upgrading WatchOS because there is only 4GB of storage. Luckily, I am on cellular, and it comes with 8GB of storage, so I do not have this problem.