Best Macbook Pro specs for focus stacking (auto-blend layers)

Almost everything in Photoshop is I/O-limited, in other words scratch disk. Especially something like this, where you will presumably have many files open and processing at the same time.

Photoshop's memory requirements vastly exceed the amount of RAM you may have installed. So the heavy lifting is in the scratch disk, with RAM mostly being a cache to the scratch disk. You should have around 500 GB - 1 TB free disk space.

However, with Apple silicon there's an additional consideration: The GPU uses shared system memory. This is important, because the GPU can use a lot and could potentially compete with the RAM allocation in Photoshop preferences. For this reason, the rule of thumb is to double the amount you would normally need. 64 GB should be considered minimum.

Also, be very careful to not set the PS allocation too high! The default is 70%, but if you get problems be prepared to dial it down a bit. This depends on your file sizes, how many files you have open, and the number of history states.