This is a false dichotomy: you can create a Zettelkasten in a single TXT file. The implementation (e.g. using multiple files, one per note) is just a convenient

This is a false dichotomy: you can create a Zettelkasten in a single TXT file. The implementation (e.g. using multiple files, one per note) is just a convenient way to see your stuff in a file listing and note taking apps, for example. But as long as you can link between notes, you're good, and a single-file Zettelkasten works just fine.