Since the currently suggested strategy seems to prove difficult for you to implement and this whole thing seems to become a kind of never ending story
I’d suggest another approach -
based upon what I understood what it is that you want to achieve:
You wanted to retain all the configurations you made to your old system - and the user data as well, right?
I’d just reinstall a fresh system,
then reinstall all the non-standard programs that you installed in addition to what is a default install,
then just restore the $HOME directory from backup.
Not the whole system - just the $HOME directory.
Avoids problems with booting, takes care of different mount options you might need for your new SSDs,
avoids having to edit the /etc/fstab and possibly more files.
Or just exclude /etc/fstab from being overwritten by replaying the backup …
(make a copy of the original in the fresh system - replay backup - replace the now wrong /etc/fstab with the copy you just made …)
I’d exclude the /etc/default/grub directory, too …
It’s really just like playing with Lego - take what you need, leave out what you don’t, what get’s in your way …