I have decided to abandon the issue.
For CSME 11, the “Temporary Disable mode” is accomplished by enabling the High Assurance Program (HAP) bit at the Flash Descriptor of the SPI chip. I assume that’s what the BIOS did. Theoretically the FD should be read/write locked so maybe that’s why it does not revert back. I wonder how it managed to change it in the first place. If it is an official option found at the BIOS then you should ask Dell how to re-enable it again. Otherwise, you’ll need to re-flash the FD region of the SPI chip in order to reverse that set bit.
That does not sound very promising. It is definitely not an user-accessible option, it was part of the advanced options that I managed to unlock. May I ask you to ellaborate a little more on the re-flashing of the FD region? I have no previous experience with that.
Edit: thank you, but I have decided to abandon the issue.
Have you tried restoring the default/stock BIOS options? That is easy enough and could help in case the BIOS causes the disablement in a different way at every boot (maybe by sending a special message instead).