I have been using Luminar for a while and I like what they are doing. The latest version introduced AI (Artificial Intelligence) to speed up processing. I am so impressed by how easy it is to replace a sky, even with complex backgrounds. WOW!
To be clear, the "cleaner" the background the better your results will be. I have included the source image so that you can see what I created using Luminar 4s amaing Sky Replacement Tool.
Head over to Luminar and learn more about their magic software!