When is the Apple Watch series going to be unsupported with updates
When would my apple watch series 6 going to not be able to update
hard to say, there have never been official stances on such things
best you can do is to look at the release of each model and when they stopped getting updates
currently my apple watch 4g did not make it to watchOS 11 you can compare it to when apple watch 3g stopped getting updates and that is about the best comparison you got and still could be off.