I have a USB hard drive. (The USB connector for that drive is actually super flaky and disconnects if you breathe on it too hard, but I don't think that's the problem here.)
I have a laptop without a DVD drive, and only one USB port. (Actually, it has more USB ports, but they seem to not work. Hmm, why is everything broken? Come to think of it, the USB cable was my fault, but I think the USB ports came that way.)
I tried to follow the instructions here, adapted to my situation: https://developers.redhat.com/products/rhel/hello-world/.
In particular, I downloaded the bootable ISO, created a virtual machine in Hyper-V on Windows 10 (Professional), and told it to boot from the ISO and install to my external drive. The installation succeed and eventually I saw a pretty GUI prompting me to log in. I then shut down the VM and declared victory.
This turned out to be premature. When I try booting from my USB drive, the boot process begins, but it never completes, and doesn't even seem to get very far. It announces the name of the OS (in particular, Red Hat Enterprise Linux 7), so it's not totally broken, but something is still wrong and I don't know what.