def METHOD_NAME(diff_output: str) -> tuple[list[str], list[str]]:
    """
    Parse the output of the `diff` utility and create two lists of files:
    - changed: files that have changed between the two folders
    - new: files that exist in the preview folder but not in the main folder
    """
    changed = []
    new = []
    for line in diff_output.strip().splitlines():
        print(f"Processing line: '{line}'")
        if line.startswith("Files"):
            # e.g.: Files /tmp/gh-pages-for-diff/_sources/meta/index.md.txt and /tmp/gh-pages/_preview/2647/_sources/meta/index.md.txt differ  # noqa: E501
            updated = line.split()[3]
            converted = convert_path_to_url(updated)
            if converted.endswith("html"):
                changed.append(converted)
        elif line.startswith("Only in"):
            if PR_NUMBER not in line:
                continue
            # e.g. Only in /tmp/gh-pages/_preview/2647/_sources/meta: examplefile.md.txt
            added = line.replace(": ", "/").split()[2]
            converted = convert_path_to_url(added)
            if converted.endswith("html"):
                new.append(converted)
    return changed, new