#Fedilab has always let you write in Markdown (MD) with your instance's converter and displays the resulting HTML, visible to everyone.
It also has its own MD rendering, which works on any instance, but only between Fedilab users. It was turned off long ago as it could break HTML formatting.
Now fixed: only real MD markers are converted and HTML stays intact. Search for "Markdown" in the settings to enable it.

Should it be enabled by default again?