So now that Minecraft 1.18.1 is out, I needed to get it running on my Surface Pro X, as built-in support does not seem to be present still.
I went and took adiantek's 1.17.1 custom json file, and initially copied all the sections that reference the java graphics libraries (anything that starts with lwjgl- and having a download url from sso.sonatype.org instead of minecraft.net) to a copy of the 1.81.1 json file. While doing this I also noticed a reference to Java 17, so I went and got the most recent Java 17 ARM64 build from Microsoft and installed that.
I was very happy to see it load up and work just fine!
But then I realized that there might be newer versions of the Java graphics libraries available compared to what was available for ARM back in September. So copied the download url from the json file which took me to the Nexus Repository Manager, and sure enough, lwjgl 3.3.0 now has a release version (vs a snapshot) with all the arm64 native files included, dated Nov 15. I went and updated my 1.18.1-aarch64 json file with the new urls, file sizes, and SHA1 checksums. I'm not sure if it'll make much difference, but who knows. Might have a few bugs worked out.

For anyone else that wants to do this, I justed used Notepad++ to edit it. Note you'll want a plugin like JSTool or JSON Viewer to make it readable in a tree view (otherwise it's one ridiculously long line).