We talked about the decaf process in a YouTube video that you can watch here. There are a couple of different processes - Swiss Water, Mountain Water (very similar processes) and a Sugar Cane Decaf that's gaining popularity. All of them basically involve soaking coffee beans in a coffee-extract solution that causes the caffeine to come out via reverse osmosis. Here are a couple of other resources about that process:
https://sadcow.coffee/blogs/news/how-caffeine-is-removed-from-a-coffee-bean
https://blog.freshgroundroast.com/how-decaf-coffee-is-done/
As for good decaf, look for a water process or a sugar cane process decaf. Both of those result in some amazing coffees.