Spoiler tag, I can confirm for me is not working. But I wasn't spoilered, I've been playing a lot of ::: spoiler spoiler Baldur's Gate 3 ::: so the answer was fresh in my mind :)

:::I don't think the tag thing works:::

I don't know but it's standing right behind you!

Using Memmy and the spoiler tags work in post, but on the main feed, the spoiler tag is not working.

So I’d say you’re using it right and the client is wrong. At least for me.

Your answer only account, for the most common variety. Many others exist.