Minecraft wiki entry for Development_versions, associated text: MC-236620 – Nether biomes don't generate correctly.
MC-236650 – Minecraft in 1.18 has 248 seeds instead of 264 seeds.
MC-236767 – Axolotls are extremely rare in lush caves.
MC-237330 – Worlds created with seed "REDApRES" (0) crash when trying to load new 1.18 mountain biomes: java.lang.NullPointerException: Cannot invoke "dfw.a(double, double, double)" because "this.a" is null.
MC-237457 – Snowy slopes biome no longer generates stone cliff feature from experimental snapshots.
MC-238003 – Stone in jagged peaks is always covered by snow blocks.