I could give you some hints,
After you donwload and install TransMac on your Windows PC, Connect the USB flash drive you want to use to fix your Mac. (If you have any data on the USB, remember to make a backup, as everything on it will be erased. Right-click
TransMac, and select the
Run as administrator option. If you’re using the trial version, wait 15 seconds, and click the
Run button.
On the left, right-click the USB flash drive, select the
Format Disk for Mac option.
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, chances are that it’s using a MBR partition, and the USB drive needs a GPT partition to work on a Mac.
On the warning message, click the Yes button to format the drive.
Enter a name for the drive, such as “macOS bootable USB” and click the OK button.
Click the Yes button.
If the formatting completed successfully, click the OK button.
Right-click the USB flash drive, and select the Restore with Disk Image option.
On the warning message, click the Yes button to confirm the data on the USB drive will be erased.
Click the browse button on the right, locate 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 version of macOS, which can be Sierra, Catalina, or later.
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Create a GPT partition on USB flash drive
If the USB flash drive is not working using TransMac, it could be still a partition problem. In this case, you want to
redo the entire process again, but this time use the following steps to use the
Diskpart command-line utility on Windows to create the appropriate GPT partition.
- 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 (e.g., 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 to a GPT partition, you can use the instructions mentioned above to use TransMac to create a bootable media, but this time skip the
steps 5 through 9, and continue on
step 10.
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 the installation of macOS.
Shall you need more information or help. Let me know.
Jimmie