what does that mean? "File converted with Indesing Markz"
Did you pay a service for converting an InDesign document to IDML?
An InDesign 2021 document to IDML ?
That should not be necessary!
What's your operating system? Is it an older Mac OS so that you cannot install InDesign 2021 on the same machine?
When online and logged in to your Creative Cloud subscription you should be able to open the InDesign 2021 document with your installed InDesign CC 2018. There is a service by Adobe that will do the conversion for you if you try to open the document.