Is iPhone SE compatible with series 8 watch

It depends on which iPhone SE? The very first iPhone SE? No. The next generation SE, yes. An Apple Watch 8 requires an iPhone which is running at least iOS 16 (current version is 16.4.1). The first generation iPhone SE cannot run iOS 16.4.1. The next generation SE can.

I have the Apple SE 2022 and the watch series 8 and the airpods third gen and they all work nicely together. I also have all three Gen's of SE and the first gen is not being updated to 16 so that is its limitation on the operating system side.

You're welcome.