You may need a bootable macOS Catalina USB drive to cleanly install the operating system or downgrade the macOS beta version. You can follow the steps here to create a bootable disk for any available version. However, since macOS Catalina is the current stable release, let me show you how to make a bootable installer drive.
Before You Begin:
Starting with Disk Drill 3, anyone can create a bootable Mac OS X drive in a matter of minutes. Make sure you have an extra storage device, which is at least 2GB in size. Connect it to any Mac, run Disk Drill and use the 'Create Boot Drive' option on the main toolbar. Now click the padlock closed to save the changes. Reboot holding the option key. If the Mac OS X installer isn’t one of the boot options, zap the PRAM and try again. If it still doesn’t work, verify that you have created the OS X installer in the same — or as recent of a version — of OS X as you intend to create on the USB flash drive. On the left pane, you’ll see all the Windows PC drives listed, right-click the USB drive that you’re intending to use to reinstall Apple’s OS X and select the Restore with Disk Image option. In the warning dialog box, click the Yes button. Use the Restore Disk Image to Drive dialog box to browse for the DMG file with the installation files for Mac OS X Yosemite in this case, and click the OK button to create a bootable USB of the operating system.
--volumeand give space.
The USB drive will be erased first, and then installer files will be copied to it. Erasing will be relatively quick. However, copying will take considerable time. Even if it is stuck at 0% or 10% for long, do not quit the Terminal window. The process is ongoing.
Note: If you have a Mac with T2 Security Chip (that is, Macs introduced in 2018 or later), first follow this guide to allow booting from external media.
After you create the bootable USB drive, the process to install it is simple. Make sure the USB drive is connected to the Mac. Next, click on the Apple logo from the top left and choose Restart. When you hear the startup sound or see the Apple logo, immediately press and hold the Option key. Select the bootable installer as the startup disk, and follow the instructions.
If you have issues, we have an extensive guide that addresses tips to fix when Mac Recovery Mode is not working.
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