To reproduce:
1. load the first 1.18 experimental snapshot
2. Create a world with the following seed: 4356972831313468911
3. Run the following command: /execute in minecraft:overworld run tp @s -905.20 84.53 150.96 -624.74 40.20
4. Make sure you are facing west
5. Notice the giant patch of clay (can't be from the river, its too far up from it.)
6. Next, run /execute in minecraft:overworld run tp @s -799.00 67.82 143.60 -952.19 39.75
7. Notice the moss and azalea on the shore.

(I also couldn't figure out how to mark the version as 1.18 Experimental Snapshot 1, so I selected 1.18 instead. Sorry.)