IMHO for Moscow to fall, there needs to be a few changes from OTl.
There could be minor - like up-gunning the Pz 3 & 4 guns earlier, or even have a 'heavy' tank.
The campaign may have started a few weeks earlier e.g. the Balkans different to OTL.
And/or Leningrad taken late July early August - before the defences were strengthened.
The attack against Moscow goes first without a distraction of Kiev. That is 'damn the flanks'.
Moscow is encircled from the south and the north.
Yes, Moscow is a big city, but we can't assume it will be a 'Stalingrad' because Stalingrad happened with the example of Moscow & Leningrad, and when the Red Army had the strength to cope.
The 'people' may react differently to the exodus of government officials.
If it does happen, then the Red Army or what is left of it, will go east and pray that the Germans don't follow it - they probably won't - instead going south-east Donets & Baku.
The Germans may achieve that objectives - Astrakhan/Arkangle (?) - but then invigorated the Red Army will start to fight back. But it pushes back the timetable in the east by at least six months.