Is the new Apple Watch SE compatible with Apple iPhone SE 1st generation?

Yes but you will need to update to ios 14;

iOS 14 compatible Devices

Apple says that iOS 14 can run on the iPhone 6s and later, which is the exact same compatibility as iOS 13. Here’s the full list:

• iPhone 11
• iPhone 11 Pro
• iPhone 11 Pro Max
• iPhone XS
• iPhone XS Max
• iPhone XR
• iPhone X
• iPhone 8
• iPhone 8 Plus
• iPhone 7
• iPhone 7 Plus
• iPhone 6s
• iPhone 6s Plus
• iPhone SE (1st generation)
• iPhone SE (2nd generation)
• iPod touch (7th generation)

Yes, The apple watch SE is compatible with 1st gen Apple Iphone SE. The only thing you have to do is just update it to ios 14.

Know more about Apple Watch SE