Hello
@mistyoptic!
In your reply box, top left, there are the tags you select for Bold, Italic, Underlined, etc.
At the end of the row, after the inverted commas, there are 3 vertical dots, more options.
The first one is the spoiler option.
Click on it, follow the instructions.
Alternatively you can use the "
" tag, without the commas.
"
" will give a title to your spoiler.
Edit: the tags are hiding the instructions hahaha