brainstorming: In what I'm writing these days, I want to include lots of diagrams / figures. Currently, I'm using Apple Pages and just drag'n'dropping screenshots into documents then publishing them to Substack (a painful process). I happen to use draw.io and excalidraw for diagramming. For a while, I was using markdown editors, but they didn't give me a WYSIWYG editing experience. I used Obsidian for a while - it did give me WYSIWYG for excalidraw diagrams, but wanted $$$s to allow me use their publishing mechanism and made it difficult to use Github Pages for $-less publishing. I keep thinking that I should just cobble together an RTF parser and use only a markdown-ish subset of features in Apple's RTF editors, but, I don't want to get side-tracked [I would use 't2t' to parse and transmogrify RTF, I think, and, use it to transpile subsetted-RTF to markdown - what's needed is an RTF-to-markdown or RTF-to-murkdown tool, I think]

pandoc

takes rtf as an input format and supports a few markdown flavors for output... I've never specifically used that combo, but sounds like it might do what you want

➕for pandoc. It can be tricky for conversions between complex forats that don't have closely matching equivalents, e.g. HTML to/from LaTeX. But for simple markup as in RTF and basic Markdown, it Just Works.