hmmm, so you're saying just install umbrelos on the external ssd? interesting idea!
Discussion
No, open both, remove internal ssd and replace with external drive's ssd so you have a 2tb internal drive.
I don't think this can be mounted internally: https://www.amazon.com/gp/aw/d/B0DG6WRD8L
One of the images shows the inside of it. Looks like a normal ssd.