Alright, for some reason, FIT refuses to work with the initialized/dumped SPI images, even though they seem healthy when checked/unpacked via ME Analyzer (MEA).
The only way to get them to work with FIT is to manually clean their initialized File Systems (MFS, EFS) by replacing those regions with the same stock ones. I used 15.0.22.1595_COR_H_A_PRD_RGN for “no-AMT-1” and 15.0.35.1951_COR_H_B_PRD_RGN for “with-AMT-1” because they include the same initial/stock MFS and EFS partition hashes.
Now, at CSME 15, we don’t need MFS and EFS to get the firmware settings before cleaning them using [Guide] Clean Dumped Intel Engine (CS)ME/(CS)TXE Regions with Data Initialization as FITC partition exists and contains the initial OEM configuration. So, replacing MFS and EFS with the stock ones is perfectly valid for getting the images ready to be cleaned via FIT.
Still, when comparing FITC settings between “no-AMT-1” and “with-AMT-1”, it appears they both use the exact same settings (AMT enabled). So both firmware are correctly configured. Which means that something else is disabling AMT. A quick look at the unpacked EFS file system using MEA shows that EFS 0000 [0x410000] > “DISABLE_MANAGEABILITY_HW (0010)” file has value 1 at “no-AMT-1” but 0 at “with-AMT-1”.
Now that you can load “no-AMT-1__fix-15.0.22.1595” in FIT, I suggest you follow [Guide] Clean Dumped Intel Engine (CS)ME/(CS)TXE Regions with Data Initialization on it and flash the result back using the programmer. Remove all power for a few minutes afterwards (leave RTC) and check if you can now enable AMT. If it is still not enabled or even possible to enable, something else is the reason. Either HW (jumper, HW fuse) or BIOS (setting).
I have uploaded the aforementioned results in this temporary link:
https://mega.nz/file/XVkwwTbR#ygQwG3M7B6VYgXaRK_ujhYpcLsVLrY1lbQHvUwV0_TI