"You Shall Not Climb!" (YSNC) is a Fabric server-side mod that takes away an ability to climb ladders from mobs that are not supposed to have it.
MC-148545 "Mobs can climb ladders" was labeled by Mojang as "Works As Intended".
Obviously, this doesn't make any sense since it's expected that most of the mobs don't use ladders deliberately.
It feels more like a side effect that is actually easy to fix, which is what this mod does.
List of mobs that can't climb ladders:
Allay, Armadillo, Axolotl, Bat, Bee, Blaze, Breeze, Camel, Cat, Chicken, Cod, Cow, Creeper, Dolphin, Donkey, Elder Guardian, Ender Dragon, Endermite, Fox, Frog, Ghast, Goat, Glow squid, Guardian, Hoglin, Horse, Llama, Magma Cube, Mooshroom, Mule, Ocelot, Panda, Parrot, Phantom, Pig, Polar Bear, Pufferfish, Rabbit, Ravager, Salmon, Sheep, Skeleton horse, Shulker, Silverfish, Slime, Sniffer, Snow Golem, Squid, Strider, Tadpole, Trader llama, Tropical fish, Turtle, Vex, Wither, Wolf, Zoglin.
No, it's only required to a server.
Maybe. YNSC provides "ynsc:cant_climb_ladders" entity type tag for compatibility with other mods.
If your favorite mod has some mobs that are not supposed to climb ladders - ask the devs to add support.
No plans.