> Not what happened here (I reserve my judgment wrt the promised TPM+PIN exploit).

Yes this is the one I'm referring to.

I have noticed it myself, it has happened to me that my system rebooted to install updates and it did not pass through the blue TPM pin entry screen at that point. That was a big red flag for me. A normal reboot always does that, even a 'hot' reboot.

> A normal reboot always [forces the TPM pin entry screen], even a 'hot' reboot.

In TPM-only mode, I only see the screen—which asks for an recovery key that serves an alternative to the TPM-borne secret, not for whatever you are calling the “TPM PIN” here—whenever I update the firmware or the bootloader (the latter from the other side of the dual-boot setup). Otherwise it boots straight to the login screen, which meshes with the measured-boot-only theory of operation I’ve described above. There’s nothing nefarious in this part, even if I think it exposes an unwisely large attack surface (e.g. the USB stack). I suspect you simply reboot so rarely you’re never hitting the happy path.