From the Wiki:

en.m.wikipedia.org/wiki/Elden_Ring_Nightreign

“released for the PlayStation 4, PlayStation 5, Windows, Xbox One, and Xbox Series X/S on May 30, 2025. It received generally positive reviews and sold 3.5 million units.[1]”

So, first, it doesn’t matter how many concurrent players it has, it sold 3.5 million so it’s not s flop.

Second, it was released on 5 platforms, you are looking at concurrent players on Steam only.