https://wccftech.com/watchos-6-works-with-apple-watch-series-4-3-2-and-1/

Great news, citizens of the internet. watchOS 6 works with all Apple Watch models, including Series 4, 3, 2 and 1.

At this point in time, one would believe that Apple might have cut support for a certain Apple Watch model in order to accommodate watchOS 6. But apparently, that’s not the case at all. If you go through Apple’s website right now, you’ll be pleased to learn that the latest watchOS 6 release works on all Apple Watch models, including Series 4, 3, 2 and 1. Of course, Apple axed support for the original Apple Watch model with the release of watchOS 5, so that stance carries over to this year as well.