Reviews, feedback and comments from collaborators/supervisors when writing in RMarkdown
In principle you can use Markdown on Overleaf (tl;dr; with a few &quot;wrapper&quot; lines in LaTeX at the beginning and end, the body of the document can be in Markdown format), but the RMarkdown layer would be an extra challenge (that is, if you actually have R code embedded in your document).
There is an interesting possibility here but it's unstable (I know the author but haven't used it). You could give it a whirl (maybe try it out with a collaborator who's up for a small adventure) and see if it seems OK for your needs. It's supposed to handle bidirectional conversion from Word tracked changes to Critic Markup.

I don't personally have a good solution for this; I either suffer the burden of propagating changes back from marked-up Word or PDF, or work with people who can handle (R)Markdown or LaTeX.