How do I move a Numbers sheet from Files app to the Home Screen?

There is no concept in iOS for files on the 'desktop' or Home Screen. The Home Screen is a launchpad for applications, and document files are not supported.

The closest you can get is to add the Files widget to your Home Screen. This will show the most-recently accessed files, but it's not the same as marking a specific file to live on your Home Screen.

You can use the Shortcuts app to create a shortcut to open the file and you can put that on the home screen. After you have the shortcut made, click the three circles in the shortcut, click the "i" at the bottom, and select "add to home screen". That will hopefully make sense when you are doing it.

Oh, nice - using Shortcuts is a possible workaround I hadn't thought about.