If you are trying to revive a Mac from the Unibody era (2008-2012) or the Trash Can Mac Pro (2013), High Sierra 10.13.6 is the final resting place for that hardware.

A modern storage architecture that replaced the decades-old HFS+, offering better encryption and faster file operations. AirPlay 2:

At its core, High Sierra 10.13.6 was defined by three massive under-the-hood shifts: