Jul 14, 2020 Bootable USB installers offer an easy way to upgrade multiple Macs to macOS Catalina, to perform clean installs of MacOS Catalina, to perform maintenance from a boot disk like formatting disks, modifying disk partitions, and performing restorations, and much more.

Now your bootable macOS Big Sur installer is ready for use. How to make a bootable copy of Catalina on USB drive? To make a bootable copy of Catalina on a USB drive, make sure it has at least 12 GB of free memory. Since your USB drive will be formatted in the process, it’s also important to back up the data you store on it.
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.
Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes. Select the volume containing the bootable installer, then click Continue.

If you want to use your USB stick with an Apple Mac, you will need to restart or power-on the Mac with the USB stick inserted while the Option/alt (⌥) key is pressed. This will launch Apple’s ‘Startup Manager’ which shows bootable devices connected to the machine. Your USB stick should appear as gold/yellow and labelled ‘EFI Boot’. How to create a bootable macOS Big Sur USB install drive. Step 1: Download macOS Big Sur. After Big Sur launches later this year, you’ll be able to download it directly from the Mac App Store.

It does not matter whether you use macOS or Windows 10. It’s just a matter of time until your device will refuse to start, which could happen for many reasons, including (and not limited to) file corruption, hardware failure, and buggy update. If the unexpected happens with an Apple computer, you can use a macOS bootable USB with the installation media to repair it.

Create Bootable Usb On Mac From Iso

This is one of the main reasons you should consider making a macOS bootable USB when your device is working properly. However, if none of your devices (MacBook, MacBook Air, MacBook Pro, iMac, Mac Pro, or Mac Mini) aren’t working when you need them the most, then you can use a PC to rescue your Apple device. You can use a Windows 10, Windows 8.1, or Windows 7 device to quickly create a USB bootable installation media to reinstall macOS Catalina or Big Sur on your Mac.

In this guide, you’ll learn the steps to create a macOS Catalina bootable USB installation on Windows 10, which you can use to reinstall or upgrade the Apple OS.

Requirements

Before proceeding, you’ll need the following:

Broken Mac computer running macOS (version 10.12, 11, or later).
A trial copy of the TransMac software.
One high-quality USB flash drive with 16GB of storage.
Copy of macOS (DMG file).

Create macOS bootable USB installation media

To create a bootable USB drive with macOS, use these steps:

Download and install TransMac on the Windows 10 device.
Quick note: This is a paid software, but it gives you a 15-day trial, which is more than enough time. (If this works for you and you want to support the developer, you can purchase the full version.)
Connect the USB flash drive. (If you have any data on the flash drive, remember to make a backup, as everything on it will be erased.)
Right-click the TransMac app and select the Run as administrator option.
Click the Run button. (If you’re using the trial version, wait 15 seconds.)
Right-click the USB flash drive, select the Format Disk for Mac option from the left navigation pane.
Quick note: You want to do this before creating the bootable media because there is a good chance that the drive was formatted using a Windows device. If this is the case, the chances are that it’s using an MBR partition, and the USB drive needs a GPT partition to work on a Mac.
Click the Yes button to format the drive on the warning message.
Confirm a name for the drive. For example, “macOS bootable USB.”
Click the OK button.
Click the Yes button.
Click the OK button.
Right-click the USB flash drive and select the Restore with Disk Image option from the left navigation pane.
Click the Yes button to confirm the erase of the USB flash drive data.
Click the browse button on the right.
Select the .dmg file with the macOS installation files.
Click the Open button.
Click the OK button.
Click the Yes button.

Once you complete the steps, you can now insert the USB flash drive on your Mac computer to install, reinstall, or upgrade the operating system to the latest macOS version, which can be Sierra, Catalina, Big Sur, or higher.

Create a GPT partition on USB flash drive

If the USB flash drive is not working with TransMac, it could still be a partition problem. In this case, you may need to redo the entire process again. However, this time you should use the following steps to use the Diskpart command-line utility on Windows 10 to create the appropriate GPT partition, and then follow the above instructions.

To create a GPT partition on a removable drive, use these steps:

Open Start.
Search for Command Prompt, right-click the top result, and select the Run as an administrator option.
Type the diskpart command and press Enter.
Enter the list disk command to view all drives connected to your computer and press Enter.
Type the select disk command followed the number assigned for the USB flash drive (for example, select disk 4), and press Enter.
Enter the clean command and press Enter.
Type the convert GPT command and press Enter.
Enter the create partition primary command and press Enter to complete the process.

Once you formatted the USB flash drive with a GPT partition, you can use the instructions mentioned above to use TransMac to create a bootable media, but this time skip steps No. 5 through 10 and continue on step 11.

After the process completes, which can take up to an hour, connect the USB flash drive and power on your Mac holding down the Option key, select the USB drive to begin installing macOS.

If you have problems creating the bootable media, you can get a USB flash drive that comes with macOS Sierra, El Capitan, Catalina, etc., on it with the link mentioned below. (I haven’t tried it personally, but it’s worth the try if nothing works.)

If your Mac suddenly refuses to boot up properly, you might need a bootable macOS USB installer to make repairs. But how do you create such a disk if all you're left with is a Windows 10 computer? Fortunately, there's a great tool that you can use for free to create bootable macOS media on a USB drive in a Windows 10 environment. This article shows you how to download a macOS DMG file, format a USB drive using a GUID Partition Table, burn the DMG to the drive and boot your Mac from the USB. All the steps except the last one are done on a Windows 10 machine.

Part 1: Download macOS or Mac OS X DMG File

The first step is to get the DMG disk image file for the version of macOS that you want. You can get a copy of the latest macOS version from Apple download portal or App Store here. There are also several other direct download sites that offer various versions of Mac OS X in DMG format rather than the standard APP format that runs on Mac. Since you're working in a Windows environment, you need the DMG rather than the APP file.

macOS DMG Download Link:

Part 2: Format USB Drive to GPT (Optional)

Updates (Dec 8, 2020): The latest version of UUByte DMG Editor is able to format the USB automatically, so this part is optional. Follow the steps only when the burning process failed in Part 3.

Create Bootable Usb On Mac Disk Utility

Mos

Catalina Bootable Disk