Why wouldn't you consider publishing on both platforms simultaneously?

I do believe that authors can publish on different platforms, including Amazon KDP in tandem with other publishing sites. One exception is when your ebook is in the Amazon Select program, you agree to keep the digital version of your e-book exclusive with Amazon.

If you are not in the Select program, you will need different ISBN numbers, one for Amazon, one for the other platform, to publish on multiple platforms.

However, those are minor issues and a book can be published on various platforms at the same time.