Even if you use a command to kill a llama spit, the llama spit will be visible and no damage will be done.

1.Use the Repeat command to execute 'kill @e[type=minecraft:llama_spit]'
2. summon wolf

As you can see, the llama stinger is visible, but there is absolutely no damage to the wolf.

Therefore, this command could be used to stop the llama's spit damage.