If you are searching for a "link" to a magical converter tool, you can stop looking. The solution is already built into your software. There is no online converter that can safely downgrade an .indd file because the complexity of the layout data is too high for a web script to handle without corruption.
The only "link" you need is the one between your Menu bar and the Export option.
Step 1: Open the file in your current (newer) version of InDesign.
You cannot convert a file without opening it first. If you have CC 2024, you must open the file there.
Step 2: Export as IDML.
Step 3: Open in the Older Version.
Important Note: The older version will convert the IDML back into an INDD file automatically when you save it. You will lose some new features (like certain SVG effects or font technologies), but your layout, links, and text will remain intact.
Issue 1: "Cannot open IDML – file is corrupt"
Issue 2: Fonts change after conversion
Issue 3: Images are missing
Issue 4: Older version won't open the IDML at all
