Sony said they sold over 4m PS5's since launch which is about 1m per month produced. They needed to make a lot more per month though since there are over 150m PS4 owners ready to upgrade.
Hate to nick pick but maths is wayyyyyyyy of.
True PS5 has been "out" for 4 months and yes, possibly 4 million units might have been sold. But the manufacture of those units didn't start in NOV. Most of these were stock piled for the launch and manufactured earlier in the year. Some PS5 have manufacture date as early as MAY 2020.
So that's 10 months of manufacture for 4million units. Thats 0.5 million units a month. This is probably ramping up, but dear COVID19 didnt help matters.
New gen consoles might be still in short supply by next Christmas.
Secondly
not every PS4 owner wants an upgrade.
not every PS4 owner needs an upgrade or can afford one.
I am PS4 owner and I honesty couldn't give a monkeys about a PS5.