Yes.
Since version 105.2.0 there is an HTML editor included as the default for editing the petition message. It works just like an WordPress text editor…because that’s what it is.
I have left the Markdown editor in place as a legacy for people who already have messages created with Markdown.
Note: if you switch from HTML to Markdown (not a good idea) or vice versa you may have to reformat your message, so choose wisely.