That only works with the rare expensive Windows To Go version. So nope, Windows on USB isn't supposed to work. If you found an article about how to do this, please share so I can check it out.
I recently bought a 10TB external drive, a WD Elements. I set up ESP and boot partitions and cloned my existing Windows to the boot partition, but I'm unable to boot off of it. When I restart my computer and press F12 to get to the boot device selection list, I'm presented with a list that includes two entries for the new drive. One specifies UEFI WD Elements and the other omits UEFI, specifying just WD Elements.
If I select the latter, my computer simply boots into my original Windows. If I choose the former, I get a message that "Your PC ran into a problem and needs to be restarted."
I'm sure that I should be providing additional information, but I'm not sure what, so I'll wait for questions.