Walmart has never had an NFC pay option. They are trying to force you to use THEIR alternative to contactless pay. The only way I have ever used Samsung Pay at Walmart was with my phones that still had MST (Magnetic Secure Transmission) where it simulates a card swipe. In those cases, it would fail to work about 1 in ten times. To be honest, since Samsung decided to get rid of MST, I have not used it at all. I put Google Pay on my watch and phone and it just works better in places that accept contactless pay.
I think Samsung is really doing their best to push people away from their ecosystem by removing all the features that made them diferent: Removed MST, watches now Wear OS instead of Tizen. Whether or not that is their intent, I am losing every reason I had to be exclusively tied to Samsung.