Not heard Last Christmas yet this year, playing Whamageddon best I've ever managed. Still don't think I'll get to Christmas Day, but happy at a strong effort
It's a chart that often gets targeted by 'protest' tracks like this, same with the sales chart. They're both fairly easy to manipulate as they are counting formats hardly anyone uses anymore.
The Download chart only counts paid for downloads from non-subscription services. So basically you have to use a store that lets you pay more than 40p (I think that's the threshold) to download an audio file.
Obviously most people subscribe to Spotify, Apple Music or similar and it doesn't count those.