The guides provided in Microsoft Learn were largely correct, aside from 2 minor but important things that took a while to find.

1. For iOS, it required that a new version number be applied in the csproj file in order for it to detect that universal linking was enabled. I've no idea why. Found the answer deep in the comments here: iOS Universal Links are not opening in-app

2. For Android, the problem was in domain verification. Firstly, the assetlinks.json file needs to be UTF8 encoded. Secondly, the SHA256 you use in the assetlinks.json file needs to come from the adb command adb shell pm get-app-links com.package.name, whereas the guidance on the Microsoft articles were to get it from the keystore. Answer was found here: How to resolve Android get-app-links Returns State 1024?