Maybe look at Quarto? Almost every project I start now begins with `quarto project create`. From there I can pivot the material into HTML, .docx, PDF, .PPTX, Typst, LaTeX, and all of them simultaneously.
There isn't an 'on-the-fly' rendering component for Quarto per se, but using the preview mode it will re-render a preview watching for file changes. A nice GUI editor for Quarto is definitely something people have been asking for. Closest equivalent would probably be Overleaf or Typst web editors?