The free space here mostly refers to 32-bit system libraries.
> Or was that already taken care of with the "app thinning" stuff a couple of years ago?
It should have been. And the update only removes 32b applications, not 32/64, if they were not doing so before I doubt they're going to thin fat binaries now.
Were apps previously installed as fat binaries with 64 and 32-bit architectures included, and the 32-bit chunk has now been removed?
Or was that already taken care of with the "app thinning" stuff a couple of years ago?