I expect the SD card is a complete bootable Linux system. This typically includes several different partitions: one for a boot loader, one for the Linux kernel and device tree, and one for the root file system. But not all of those partitions are formatted so that they can be read or written directly by the file system software in a desktop computer. Therefore you usually need to use a tool capable of a sector-by-sector SD card image directly to the card, without going through a file system - that's what the imageUSB tool is doing, I expect. The Linux/macOS "dd" command does the same thing.
ETA: yes, it looks like the imageUSB tool is expecting you to have a USB-connected SD card reader/writer. But depending on how it detects the device it may or may not work with a built-in SD card slot. I'd try it and see, but please double check before you say "go", to make sure it's going to write the image to the correct device.
ETA: if imageUSB doesn't work with a built-in SD card reader/write, you might want to try this, which I've used successfully to do this kind of thing: https://www.balena.io/etcher.
ETA: yes, it looks like the imageUSB tool is expecting you to have a USB-connected SD card reader/writer. But depending on how it detects the device it may or may not work with a built-in SD card slot. I'd try it and see, but please double check before you say "go", to make sure it's going to write the image to the correct device.
ETA: if imageUSB doesn't work with a built-in SD card reader/write, you might want to try this, which I've used successfully to do this kind of thing: https://www.balena.io/etcher.
Roon (Mac Mini), Wilson Benesch Full Circle, Expert 1000 Pro CI, Kaiser Chiara
Warwickshire, UK
