I booted into a 16GB live USB of 20.04 that I created in my computer's already installed operating system, Windows, and installed mkusb there and followed the directions given here for a separate 32GB USB drive. I made it through all the steps, except for the one that says "work done."
Now the progress bars have been stuck in their places and the command line hasn't updated for over an hour now.
Here's a screenshot showing the progress bars:
I have a moderately-powered computer and I had no previous problems flashing the iso onto the non-persistent 16GB I'm currently writing this on in Windows.
I decided to try mkusb from a live Ubuntu USB after struggles with making the persistent drive with Rufus and other Windows applications. I chose 95% of remaining space for persistence because I don't imagine needing any usbdata space.
Maybe it's just stuck making that big 20+GB persistent space?
Edit: I'm debating if I should just take the USB out with this window still up and try booting it to see if it works, and wiping it and trying again if it doesn't - try using a Windows program again maybe... Would it be possible to stop this last process it's running (flushing file system buffers) without corrupting it or preventing it from booting?