I think they'd been working on it for many years beforehand. Getting the software stack ready for a new architecture, especially one where there is a lot of 3rd party code you can't touch, is a lot of work.
After all, step one was porting their darwin kernel in 2007. Then the 'Unified Platform' work of 2017 made the userspace work on ARM... Then 2020 they released an ARM desktop product... So it was a lot of years!!
I think they'd been working on it for many years beforehand. Getting the software stack ready for a new architecture, especially one where there is a lot of 3rd party code you can't touch, is a lot of work.
After all, step one was porting their darwin kernel in 2007. Then the 'Unified Platform' work of 2017 made the userspace work on ARM... Then 2020 they released an ARM desktop product... So it was a lot of years!!