Thanks or the update on this issue. Really appreciated!

For what it's worth whilst you may not be able to subscribe directly within the Google Calendar app, clicking on the click from your website, even if you are on a mobile, does add the calendar - so the instructions on your website are valid regardless, they just need the extra wording, to complete the process and ensure the calendar then actually shows.

That said, I suggest before adding the wording you give it a try/test on Android yourself and you'll see what I mean.