WetGeek I happen to have an SSK NVMe enclosure that suports USB 3.1 and USB C. ... I'm still fascinated by the idea of a working OS on a tiny flash drive. Maybe that idea will turn out to be less than practical, and I might fall back on that NVMe as an alternative.
Either way, keep in mind that you are setting up a dual-drive, dual-boot (or maybe multi-drive, multi-boot) and you are going to have to pay attention to what you are doing when you set up the external drive lest you tangle the bootloaders. I do my usual ID-10-T avoidance routine, and install on the USB with all other drives unplugged.
I use Windows on my laptops, but I have a Solus install on an external 64 GB USB 3 "thumbnail" drive.

It isn't quick (200 mbs) and like all "thumbnails" it runs too hot for my taste, but it works when I need it. I keep it in my laptop travel case, and update it every month or so.
I've also used a spare NVMe M.2 drive in a case for that purpose, but it was clumsy for a laptop, so I don't do that any more.