Today I did some experimenting and first shutdown my test system, which is a small NUC with easy top access to the m2.nvme ssd. I replaced the ssd with a fresh stick and did my testing. When done testing, I shutdown and replaced the ssd with my old daily driver ssd.
You guessed it; it would not boot and UEFI showed no bootable drive. The last time I did this, I just booted a live Debian ISO, installed timeshift and restored my most recent snapshot. That worked then but not now.
This time I boot up butterknife ISO, which I had used for the original install, but this time after I setup WiFi, I went to the chroot recovery option. It dropped me into a session where I was on my non-bootable ssd and everything looked good.
I then did a grub-install /dev/nvme0n1 and once it completed I just rebooted.
It worked. So I can recommend the chroot recovery option on Butterknife. Thanks, Drew