New SSD has successfully cloned OS, but won't boot (Non-system disk)

Fully operational perfectly running OS and Programs on old SSD. Macrium showed successful cloning (verified) to new SSD. Removed old and installed new. Non-system disk error.
Used W10 ISO CD to get to repair mode. Repair failed.
Went to CMD prompt (still using ISO disc) and used diskpart. All volumes showed, but all letters wrong. Used diskpart to change all letters and remove letter from small Recovery volume. All letters showed as correct on new SSD (and on second SSD, which was not involved in this switch of new and old System+programs SSDs). Reset BIOS to boot from Disk 0 (new SSD). Boot attempt produced Non-system disk error.
Used ISO to get back to diskpart. All volumes showed wrong letters again (same ones). Tried again. Repeated startup attempt. Non-system disk error.
I thought this was going to be easy: Clone old System+data SSD to new SSD, swap out old for new, boot, and the system runs perfectly from the new SSD (which now has a new lease on life). WRONG.
Please offer suggestions (other than re-install old SSD and carry on until it fails). I love and depend on this forum.

Please take care in this dangerous period of our lives.
W10 1909

Used Macrium Reflect Free (latest v.). Cloned and verified. 240 GB to 240 GB.

Here's the OLD disk, plugged into the computer I'm using temporarily. As you'll see, the letters for disk 2 have been altered by the process of just plugging the old SSD in to the comp in an external drive enclosure,

You mean Image the old to my spare internal, then Restore to the blank new (in a USB external drive encl), then swap the old and new and boot? Easy enough, now that I'm back on the old (which booted perfectly -- I love it, but I don't trust it any more after years of heavy writing, re-writing, etc.). Please confirm that I understand you correctly, Caledon.

Wow, Caledon in ONtario, eh?

Berton said:

For some reason your clone missed getting the boot files [...] just want to keep the Win7 available as I have done with a WinXP computer.

You're a braver man than I am, Berton, with the XP machine, but I, too plan to keep my old Win 7 Pro machine available to run as needed for as long as I can.

Thank you for taking the time to post. I have used Macrium Reflect Free to image the old disk, and then to "Restore" that image to my new SSD, mounted as an external. Worked perfectly when I installed the new one and booted. I appreciate your time and your ideas.

- - - Updated - - -

Caledon Ken said:

Yes. Backup to somewhere and then restore to new SSD. [...] I have drives that have been in service years. Of course I'm a huge fan of backups.

Worked Purr-fectly, my Ontario friend! I had a bit of trouble figuring out how to redirect the image-restoring process, which defaults to putting the image right back where it came from, but I got it after a bit of clicking around. Then I had a bit of trouble figuring out how to safely disconnect the external in the face of W 10's determined efforts to keep it busy. Rebooting didn't release it, nor could I free it in Disk Management, but shutting completely down and then detaching it did the trick. When mounted, the new disk booted perfectly, and it's now the Main Disk on the computer I'm using to write this grateful response.

I will now happily join the list of supporters of imaging over cloning, and cancel my membership in the Cloning Camp.

Thank you for taking the time to post, and for following up until I had the solution.

Now my appreciation for the value of backups is even greater than before, because I know another purpose to which they can be put when needed.

It IS huge,eh? Few Americans know that you could put a couple of Texases into Ontario, and still have room for Massachusetts. I'm in Kingston. "Greater Metropolitan Kingston," actually: I'm a country boy, up in Elginburg, about 15 k north of the city. (I don't think this conversation is appropriate for the Forum, but maybe they'll let me get away with it because I'm a newbie. I won't do it again. I'll find out how to use the PM function.)

Anyway, I hoped my posts would help somebody other than just me, and I would welcome questions from Forum readers who have difficulties similar to the ones I had with moving my OS from an old drive to a new one.