Pairing
The Apple support page Apple Watch Series 6 - Technical Specifications (UK)
says "Apple Watch Series 6 require an iPhone 6s or later with iOS 14 or later."
I have bought an Apple Watch Series 6 and tried to pair it with an iPhone 6s with iOS 15.7.3 but it refused to pair and tells me that it needs an iPhone 8 or later with iOS 16 or later.
iPhone 6s, iOS 15