Find Xur in his old location from before the Season of Opulence on Nessus. Climb the tree at the north end of Watcher’s Grave to find him.
You’ll need to head to a new location to find Xur on Nessus in Beyond Light–which is actually his old location. Spawn in at the Watcher’s Grave transmat zone and ride your sparrow north. You won’t find Xur waiting on Calus’s barge as usual, which isn’t hovering over the area but has since crashed; instead, Xur is up the big reddish tree on the right side of the area, near the pathway toward The Tangle. Climb up and find him hanging out on one of the branches overlooking the area.