Ok, the times counting for GFA etc is a bit more of an incentive to take part.
Particularly since the Champs qualifying HM standard got so tasty. Sorry to hear about your illness/injury. Would be good to catch up on an actual start line again this year.
The times count for GFA, according to their FAQs.
They are also pushing their app, but according to this https://www.runnersworld.com/uk/news/a33816236/virtual-2020-london-marathon/ you can submit running watch / Strava as evidence. I hadn't even thought about it until you mentioned it. Sod running about with my phone