My Apple Watch keeps getting disconnected from the Bluetooth connection on my iPhone. I’m having difficulty connecting other Bluetooth items as well. How to fix that?

For Apple Watch to pair with an iPhone you need

• To use your Apple Watch Series 3 or later with watchOS 8, you need to pair your Apple Watch with an iPhone 6s or later with iOS 15 or later. Setup assistants on your iPhone and Apple Watch work together to help you pair and set up your Apple Watch.
• To use your Apple Watch Series 3 or later with watchOS 7, you need to pair your Apple Watch with an iPhone 6s or later with iOS 14 or later. Setup assistants on your iPhone and Apple Watch work together to help you pair and set up your Apple Watch.
• To use your Apple Watch Series 1 or later with watchOS 6.2, you need to pair your Apple Watch with an iPhone 6s or later with iOS 13 or later. Setup assistants on your iPhone and Apple Watch work together to help you pair and set up your Apple Watch.
• To use your Apple Watch Series 1 or later with watchOS 5, you need to pair it with an iPhone 5s or later with iOS 12 or later—Apple Watch models with cellular require an iPhone 6 or later. Setup assistants on your iPhone and Apple Watch work together to help you pair and set up your Apple Watch.