Question of understanding: QT reference / 32-bit QuickTime Support Ending

Greetings,

I understand that some codecs of Quicktime might be gone in AME because they are no longer supported.

However, spefificly I do not understand two issues regarding my mostly used codecs/workflows:

We use very often Quicktime reference files exported from Avid Media Composer.
Now it shows only black in Adobe Media Encoder, even if the DNxHD/HR is used.

DNxHD/HR is listed as 'native video import', so I would assume it should work.

Is it because it is used within a .mov container?

And secondly: Why is png no longer supported for export, while it is supported for import?

Thank you very much