diskutil listĮnter the commands given below to create the USB flash drive installer. Use the command given below to determine the identifier for the flash drive. In other words, there is more than one way to create a USB flash drive installer from a Snow Leopard ISO file. This differs from the flash drive created using the Disk Utility, which used the Master Boot Record scheme. Note: This flashdrive will be using the Apple Partition Map scheme. Finally, click on the Restore button in the popup window. In the popup window, select restore from Mac OS X Install DVD, as shown below. Highlight the name Untitled, then click on the Restore button on the top of the Disk Utility application window. Use the Disk Utility application to erase the flash drive, as shown below. Use the Finder application to mount the Snow Leopard ISO file. The Snow Leopard ISO file was the same as discussed in this answer, which should be the same ISO you have linked to in your question. The flash drive needs to be at least 8 GB in size. The procedure should be the same for Catalina. This was tested using an iMac (21.5-inch, Mid 2011) 2.5 GHz Intel Core i5 with MacOS High Sierra 10.13.6 installed. Creating a USB Flash Drive Installer from a Snow Leopard ISO File