Aha! That got it. Three colons. Spoiler, then the text for the spoiler listing, an enter, n closing `::: and then it works. It doesn’t work without the enter before the spolied text, which is just confusing and annoying imo. The >! Markdown is so much better.
But! You can enter anything after the initial ::: spoiler as the text to show before clicking
extratesting
It’s working on mobile browser for me, but not on jerboa. Jerboa doesn’t seem to recognize several markdown notations.