Hi and welcome to the forum
You should know that Windows PCs are not designed to boot from external media such as hard drives and flash drives. This is a limitation of Windows and is also part of the licensing agreement they have with PC makers *including Surface which is a division of Microsoft*.
That being said, if you Google it and also look around at YouTube, lots of people are doing this for one reason and another such as better protection from viruses/malware, privacy protection (in W10 primarily), and over-all security. Some folks have kids or grandkids in their house and when they leave, they don't want them to be able to use their laptop at all. Pulling the hard drive where the Windows 10 OS normally resides clearly makes that work if you have to have external media plugged into the laptop to make it work. This is analogous in the old days where parents who were owners of desktop PCs would lock up their keyboards and or mice in a locking file cabinet or gun safe. You should also know that you basically have to Hack your W10 in order to do this with the various tricks out on the Internet. When you do this, and you encounter a problem with it; bear in mind Microsoft will not assist you with it since they don't support it, and also considers it a violation of the W10 EULA (End User License Agreement) for the software on your Surface laptop. If that weren't enough to dissuade you, and you return the Surface to your place of purchase, say Best Buy or Staples to get an In-Warranty repair, they won't touch it with your OS on external media for all the above reasons. You could remove the SSD drive or HDD drive from the Surface and take it to their repair centers or ship it back to Microsoft, but the act of removing the Drive with the W10 OS on it, most likely will Void your factory warranty (if it's less than 1 yr. old), and they will only fix it if you pay for a new drive (SSD or HDD)!!
Depending on the
EXACT Surface model number, you may also have one that has the SSD embedded in the Motherboard circuitry; in other words it's a Chip that's hardwired into the Circuit Board and therefore
NOT removable.
I haven't seen any Surface laptops with this configuration but have read about them, that's why I mention it. Also, I've run into at least 2 smaller laptops and netbooks (including my Dell Mini Netbook 11) that have SSDe (or Solid State Drive chips) in them. Those of course can't be removed for either repair or modification as in your case where you want to run W10 from a flash drive external to the computer.
Don't get me wrong; you may still be able to run your Surface in this fashion, but you are going to run into a lot of headaches if something goes awry.
Best of luck,
<<BIGBEARJEDI>>
