[Quoth]

I suspect there is a way, but not via KDP, to publish PDF on Amazon. The customer doesn't get a PDF, but it's a PDF inside. There are maybe azw* and KFX fixed layout (Print Replica) on Amazon that are really PDF.

Historically Amazon Print Replica (fixed layout) was only for the App (inc Fire), not eink Kindles, but the Scribe might work.

The bigger publishers do not use Amazon KDP.

EDIT / PS:

I did get a 14.25″ Nxtpaper 3.0 tablet since I wrote before (TCL NxtPaper 14) and first time in 30 years of portable gadgets I can now read ANY document on a portable device. The Kobo eink 7″ Libra or 8″ Sage is still better for reflowable novels, mostly due to size.
I once nearly bought a Sony DPT, and glad I didn't. The two 10.3″ eink were not good enough (reMarkable and Elipsa) and are now given away. The 9.7″ Kindle DXG was always pointless for PDF. Too low resolution (150 dpi), too small and too slow.