Minimum 64GB , but 256GB or more is recommended for a smooth experience. 2. Prepare the External Drive
You'll need an external drive with at least of space, though 128GB or more is recommended for a smooth experience. How to use an external storage device as a Mac startup disk install macos on external drive
Hold the Option key (Intel) or Power button (Apple Silicon) during startup to choose your drive. Minimum 64GB , but 256GB or more is