I searched and found a problem at images ported from odp to pptx dark, but the question was closed. I found a solution at Dark pictures in ODT document from LibreOffice - Microsoft Community, and was able to provide the URL in the comments of the close question.
Will the closed question eventually disappear from the forum? If so, that’s one link to the answer that will disappear.
On a related note, how does one request that the question be re-opened? I think it would be a good idea to replicate the solution as an answer to the question (properly cited) in case the solution disappears from where it currently resides. That can’t be done in the comments.