Editing Openai/691c64c3-536c-8008-a507-c542c3a174f3 (section)

==== 2. Full solution: Install macOS 26.1 itself on the external SSD ====

If you want everything (apps, libraries, system) on the external SSD, use it as a separate startup disk.

===== A. Prepare the external SSD =====
# Back up anything important on that SSD.
# Open Disk Utility.
# Select the external SSD device (top line, not its volume).
# Click Erase… - Format: APFS - Scheme: GUID Partition Map - Name: e.g. macOS-External.

===== B. Install macOS 26.1 to the SSD =====
# Open Install macOS 26.1 (from Applications or the App Store).
# When it asks where to install, click Show All Disks and choose macOS-External.
# Let the installation finish (the Mac will reboot a few times).

===== C. Boot from the external SSD =====

On Apple Silicon:
# Shut down the Mac.
# Press and hold the Power button until you see “Loading startup options”.
# Choose macOS-External.
# Click Continue.

Now, when you’re booted from the external system:
* All apps you install (App Store, .pkg, .dmg) will be on the external SSD’s system volume.
* Your internal macOS stays mostly untouched (good for testing or keeping it “clean”).

You can later set the default startup disk in
System Settings → General → Startup Disk.