I own the Scandinavian UHD release of Tenet. I can confirm that it is available as a 3-disc Steelbook release (thank you, Father Christmas!), but this is a “Limited Edition,” and there is also a standard Amaray case available for this combination. (I have seen it at stores.)
As for the Blu-ray release, I have seen it at stores and I presume it is a 2-disc set, without any DVD Copy.
There is an image of the backcover available, but it may not represent the final artwork; however, this one mentions specifically that there are only 2 discs: image.