Yes - markdown is about portable text. This and most such tools should be a folder structure of .md files. You can then open that same structure in e.g. Ulyss

Yes - markdown is about portable text. This and most such tools should be a folder structure of .md files. You can then open that same structure in e.g. Ulysses or VSCode. iCloud storage is “built in” on the Apple camp and OneDrive or Dropbox are ubiquitous enough on the Windows and cross-platform camp.