Existing 3rd party software migration

Solution 1:

To the end user, Apple will be doing it the same way as they did for the transition to Intel.

New apps will be released with effectively, 'two apps in one' - originally known as a fat binary or Universal app - which can run on either platform. Legacy apps will run under an invisible translator, originally known as Rosetta & now, unsurprisingly as Rosetta 2. Universal will be, by the same token, Universal 2.

There's Apple's main press notification at Apple announces Mac transition to Apple silicon but The Verge has a more consumer-friendly explanation

That’s where Rosetta 2 comes in: It’s an emulator built into macOS Big Sur that will enable ARM Macs to run old Intel apps. Rosetta 2 essentially “translates” instructions that were written for Intel processors into commands that Apple’s chips can understand. Developers won’t need to make any changes to their old apps; they’ll just work. (The original Rosetta was released in 2006 to facilitate Apple’s transition from PowerPC to Intel. Apple has also stated that it will support x86 Macs “for years to come,” as far as OS updates are concerned. The company shifted from PowerPC to Intel chips in 2006, but ditched support for the former in 2009; OS X Snow Leopard was Intel-only.)

Rosetta 2 will allow apps built for Intel chips to run on Apple’s new processors without any work from the developer You don’t, as a user, interact with Rosetta; it does its work behind-the-scenes. “Rosetta 2 is mostly there to minimize the impact on end-users and their experience when they buy a new Mac with Apple Silicon,” says Angela Yu, founder of the software-development school App Brewery. “If Rosetta 2 does its job, your average user should not notice its existence.”

Solution 2:

Two notable differences between 'old' Rosetta and 'new' Rosetta are:

1. Rosetta 2 will 'pre-compile' its translation before the app is launched. The old Rosetta would 'translate' PPC code to Intel anew each time the app was executed.

2. PPC CPUs were 'Big-endian' (the order in which multi-byte words were stored), whereas Intel and ARM chips are both 'little-endian'. That removes one of the major headaches and causes of problems in translation.