I had constructed a nether hub of some sorts a while back to connect my base to a village. On my way over I noticed some things had changed. (I had created this hub way before 1.16) The portal was missing, (I had created a new one, the one you see in the screenshot) and the terrain had morphed into a soul sand valley. I had already explored this place before the nether update so it shouldn't have changed. The destination in the over-world and the village have not changed, just the nether near my original portal. The stairway I had created was also partially cut off, right where the soul sand valley begins.