this says in 2006 they sold 4.5 million computers, and implies that this is a recent high.
so... 12*4.5 = 54 million as a guess at an upper bound?

https://www.forbes.com/forbes/2006/0130/043.html

So here's the fun thing:

The Nintendo Wii sold 101 million consoles.
The Xbox 360 sold over 81 million consoles.
The Nintendo Gamecube and Wii U add another 21 million and 14 million consoles.
All those consoles are PowerPC!

WHICH MEANS that Apple only managed to ship enough PowerPC Macs to about match the Nintendo Wii.
And all three PowerPC Nintendo consoles easily outsold all PowerPC macs.

So if you had a PowerPC chip in your house, it was most likely Nintendo's fault, not Apple's.