Thought you might say that. «* my interest...is over*» That’s the same website that has Manchester at 2 million 875,000 LOL. If you click on Sheffield it immediately gives two different figures for Sheffield including 555,000, more than I thought but not, 722,000.
Sheffield Urban area includes Rotherham, another Championship football club drawing support from the same «* catchment area*» ( magic word)
You should have a look at Sheffield City council stats, a bit more reliable I guess