Thanks for clarifying. Since you’re using the Windows desktop version and can’t save to OneDrive, the issue could be with file permissions, OneDrive syncing, or file corruption.
First, make sure Office is fully updated via File > Account > Update Options > Update Now. Try saving the file locally on your PC in a simple folder like Documents. Check that OneDrive is running and signed in, and that you have enough storage and proper permissions. If the file still won’t save or images revert, I recommend creating a new blank presentation and importing your slides via Home > New Slide > Reuse Slides to avoid corruption, then save the new file locally.