Single-biome worlds generated using Nether biomes use grass blocks for the surface.

When playing on a 1.18 server with a 1.17 client, rain appears in snowy and dry biomes if there is a cave biome below the surface biome.

Rain and snow fall on the same blocks in a certain height range

Non-cave biomes overlap at their edges.

Snow levels in various biomes are higher than before

Rain falls over parts of badlands biomes