Apple Watch Series 6 doesn't pair to my iPhone 6s Plus

I bought a iwatch 6 but it doesn’t work with my iphone 6 plus. The device advices to upgrade my phone - it works now on iOS 12.4.8- but it seems that there is no update available. So I cannot go further.

i am planning to buy a new iphone 12 ( or 11): do i have te wait or is there a possibility to use the watch?

[Re-Titled by Moderator]