I suspect your plan might be safer and less of a pain than pvmove. I’ve just never done that before so I can’t say for sure.
Be sure you can open and mount the USB ssd after the first dd. Also check the status of the disk size of the luks container. I’m assuming your dd’ing the encrypted partition not the data inside.
Look into pvmove. I’d take a backup with dd but try to do the actual move with pvmove. This might involve multiple steps if you can’t have both nvme’s installed at the same time. In that case I hope you have other drives.
Edit: I think what you’re doing won’t be a disaster because you’re not writing anything to the old nvme so that data is still there. So you won’t bork anything if the new drive doesn’t work.
I recently read that luks containers don’t actually know their size they will always adapt to the size of the entire disk (it makes shrinking them dangerous). So you should be good unless your SSD is bigger than your new nvme.
Very curious about how this goes. It might not work but it won’t wipe the original nvme. I’d love to hear how it goes.