I believe that limitation only applies to older versions of Special K. Latest versions that has DirectX 12 support (e.g. from the below thread), should work just fine with Waitable Swapchains.
It’s at least how I play on my G-Sync monitor – with Waitable Swapchains enabled.
These are my general go-to configuration in most games (though some might not work properly with 4 buffers):
