I hope you take my feedback with an open mind as I don't mean anything personal. Your article is an example of people who look at things through their own lens rather than the general one.

I'm certain 95% of the population would be using Apple or Android, and the instructions on the Gov UK site are made for the majority, not for the edge cases.

My comment falls exactly within that, for most people, they define email as Gmail or Outlook. There are people who use Proton, iCloud, or personal domain emails, but the instructions will always mention what the average person would know and identify.