Nope, you need a Mac because that's the only way to access the notes database. On iOS, you can't access it because iOS is more locked down. You can try using Shortcuts to export your notes, but it's frankly buggy and it's has only worked properly for me on a couple OS versions. Theoretically, you could create Markdown versions of the notes, since there is a "Make Markdown from Rich Text" action, but it has never worked for me on iOS (and only sort of works on macOS).
If you will have access to a Mac in the near future, I'd manually copy over notes as needed. If you won't, then try Shortcuts. Alternatively, you can drop and drop a note from Notes into Files, which will save it as an .rtfd on iOS 18. You can then try to find an .rtf to .md converter. Or try Shortcuts convert RTF to HTML, which has worked mostly reliably in my experience—Obsidian can import HTML if I recall correctly.