PSA about spoilers, tagging and muting before the next XIV update, covering two things:

what "mute this conversation/thread" does and doesn't do (it doesn't stop people from seeing a thread)
how you can actually prevent people from seeing a thread with spoilers

Thread

"mute this conversation" doesnt work the way most people think it works. It doesnt stop showing a thread on a person's timeline if they mute it, it only stops you personally from getting notifications from likes/replies/RTs if you're tagged in that thread. try muting this thread!

however, if you use a hashtag like #ffxivspoilers or whatever else in the first post of a thread, someone can mute that hashtag and not only will it hide that first post but the entire thread will be hidden too, whether the posts below it use the hashtag or not. And there's more!

This also includes *untagged replies*. People, including replies between two people you follow that you'd normally see, can respond to a thread and you will not see the replies to it whether they use a hashtag in their reply or not. The *whole thread* will be hidden.

Which means, in summary, you can make a thread with an initial post like "Thread with 5.45 spoilers below, please mute #ulfatalksaboutMisija" or whatever and it will genuinely hide the entire thing, but it totally depends on communicating that and people muting it.