Open trapdoors, which were a barrier to mobs in 1.17.41, are now passable. I started using trapdoors back in 1.16 as walkable fence gates. I could walk across them, but mobs couldn’t pathfind across them. This worked all the way up until 1.18, and now my horses, llamas and sheep are just walking right across them.

Absolutely love the update, though. It’s beautiful.