I have had a fairly generic response from support:
What you’re seeing is expected behavior with DxO PureRAW 6 “High-Fidelity DNG Compression” output: those DNG files use an advanced lossy DNG compression method, and some Windows applications (including Microsoft Photos and Windows thumbnails/preview) may not support that format-so they can show no thumbnail and Photos can report “unsupported or corrupted” even when the file itself is fine.
From our side, this aligns with our documented limitation that DNG files using lossy compression (Lossy DNG) are not supported by some software environments.
I have now let them know my camera (OM-1 Mk II) and lens (OLYMPUS M.12-100mm F4.0) and sent them both the original .ORF file and the compressed .DNG file that my Windows Explorer can’t read. I have pointed out that my Windows 11 installation and driver files are all fully up-to-date.
Hopefully they will be able to help in some way. In the meantime, I’ve also raised a ticket with my photo editing software house to request support for these files in a future update.
EDIT: Interestingly, FastStone Image Viewer 8.3 can see and read the compressed DNG.