Spoiler blocks will work for both lemmy and PieFed…the ones formatted like this:

::: spoiler Spoiler Title
spoiler-y stuff here
:::

However, it makes the spoiler be on its own line, in its own collapsible section. That is often inconvenient if you just need to spoiler out a character’s name from a sentence or something like that. I don’t know rust nor have the inclination/time to learn, but I do know python. So, I added the functionality to PieFed and then chimed in on the lemmy github issue to try to influence lemmy to incorporate the feature as well. However, it seems like they are content to let the github issue sit open indefinitely instead.