Make sure the dir you are mounting to exists. If it doesn’t, create it with:

mkdir /mn

There’s a few ways to go, I have used dd in the past to clone the existing drive out to a disk image on a USB SSD, then installed the new SSD in the system and did the process in reverse (and then used gparted to expand the partitions out to size).

There’s also cloning devices that can do this but I’ve only ever done that with traditional 3.5" and 2.5" disks, not m.2.

Whatever you do, make sure you have a backup of your important data before you make any attempt.

I set this up for production on a factory floor for others to use. It’s nice, works extremely well once set up. Importing and exporting images could be easier.

Seconded. I’ve been running the result of this ansible deployment for a year now, loving it