Can I wear my apple watch SE 40mm in the pool when swimming?

I have worn my Series 6 swimming and all is fine. They're pretty cagey about that "water resistant not water proof" warning. That is there so that they have an excuse not to repair it for free if there is water damage. It's a "use at your own risk" thing.

Swim with your Apple Watch – Apple Support (UK)

You can, but personally, I wouldn't.

Read this link about splash and water resistance of Apple Watch --> About Apple Watch water resistance - Apple Support