If you're using a Surface Pro X with a Surface Dock, you might be finding that you can't update the firmware on your Surface Dock, and you're not alone. As spotted by Windows Central and noted in a Reddit thread, users are seeing an error that says, "This installation package is not supported by this processor type. Contact your product vendor."
Obviously, the processor type is ARM64, and the Surface Pro X is the only ARM64 Surface, and the only ARM Surface with a modern Surface Connect port. As one person noted on Reddit, you can always use an x64 Surface (literally any other Surface) to update the Dock, assuming that you've got one lying around. One user didn't realize that ARM64 and x64 are different things, which is more of an issue with Microsoft's messaging around the product.
In the most recent update for the Surface Dock, Microsoft added support for the Surface Pro 7 and Surface Laptop 3, with the Pro X notably missing. The Surface Pro X is, however, listed as a supported device on the Surface Dock listing on the Microsoft Store. Presumably, Microsoft will release an ARM64 package for the Surface Dock update sooner rather than later.