So I try a 'legacy' approach per the cryptosetup wiki:

linux-p22i /root# cryptsetup create back5 /dev/sdi1
Enter passphrase:
(which I did; just got newline)

linux-p22i /root# cryptsetup status back5
/dev/mapper/back5 is active.
  type:    PLAIN
  cipher:  aes-cbc-essiv:sha256
  keysize: 256 bits
  device:  /dev/sdi1
  offset:  0 sectors
  size:    976768002 sectors
  mode:    read/write

***which seems correct to me***

linux-p22i /root# l /dev/mapper/
back5@                                              cr_ata-WDC_WD1002FAEX-00Z3A0_WD-WCATRC268610-part1@
control%                                            main@

Now. How do I or what do I mount?  I can't use /dev/mapper directly.
I have no success trying to mkfs /dev/back5.

This must be a common problem but I don't find
it addressed in the opensuse forums.

 
The mapper path created is "/dev/mapper/back5".This is the plain text path you use to access stuff stored in the encrypted volume.

Just to be safe the default options of cryptsetup are the same as the ones you used when you were using losetup,run the following commands to see if they will recognize the file system on the volume.

blkid /dev/mapper/back5

what seem correct to you may not be.With slightly different encryption options,its even possible for blkid among other tools to see valid file system giving you more hope you have used correct options and you could end up corrupting your data if you write to them.

I think the safety thing to do is to go back to an old system where the volumes worked,copy the data off of them and then create a new cryptsetup volume on the device and then move back your data.