I don't think there any reliable figures out there. But the ones that you do find by digging a bit on Google and same regional sale figures paint the sales of the mid-gen upgrades as not particularly high.
My personal guess would be that the PS4 Pro has sold about 10 million and the Xbox One X has sold around 5 million.
There's not enough of a market to bother releasing PS4 and Xbox One titles that only run on those pieces of hardware. That is, I don't think Sony and Microsoft feel its worth it.
Lifetime Sales Predictions
Switch: 151 million (was 73, then 96, then 113 million, then 125 million, then 144 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 57 million (was 60 million, then 67 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima