And this Zeiss Jena Sonnar 180/2.8 was actually initially sold for 35mm, starting with the Contax in the 30s (that's why they call it the Olympic Sonnar), in the 50s for Exakta, Praktina and M42. All had a removable lens mount which was originally from the Contax to add a mirror adapter. Soon 3rd party makers figured out this lens worked well on the Pentacon Six (6x6) and offered adapters (remove the original mount, simple screw, add the new mount).
Since this was popular, Zeiss Jena made it then for a long time natively in the Pentacon Six mount, without the old removable mount.
I have one for my Praktina, and still looking for the adapter to use the same lens easily on my Pentax 645, since this is easy adapted from Pentacon Six. For now I saw the adapter only for stupid prices, but here someone found it cheap:
https://blendfx.com/csj-sonnar/