What's the best way to flash an ISO onto a USB partition?

If your goal is to run Linux from a USB flash drive, definitely back up everything first! Flushing the whole drive will modify its MBR, which means you might lose other data on it. The easiest route is to wipe the USB drive clean and write the install ISO directly to it, using tools like Rufus on Windows or dd on Linux. If you can, using a second drive could save you a whole lot of hassle!

You can technically copy an ISO file to a USB partition, but keep in mind that flashing an ISO means overwriting the current partition structure. If you're looking to install Linux to that 32GB partition, it's usually safer to flash the ISO to a separate USB stick, boot from it, and then select your 32GB partition as the target for installation.

First off, are you sure the ISO you're using is designed to be used with a partition and not the entire drive? That's an important distinction, as flashing an image can alter the partition table and potentially overwrite existing data.