I don’t think the editor is a choice made by your frontend, it’s a choice made by which methods you choose to use. If you use a markdown editor then you probably need a markdown to HTML conversion library.
If you use an object based editor then you will need that editors native client to convert to html
Or you can choose an HTML editor, but generally storing raw HTML in the database is frowned on, especially from a headless CMS perspective since the formatting may not fit for multiple “heads” like web, mobile, ect.