Step 1: Download the downgrade FW update tool
First, download the FW update tool specifically designed for Thunderbolt Downgrade NVM31.
Step 2.1: (For onboard TBT) Enable Thunderbolt function
Access the BIOS setup and ensure that the Advanced > Thunderbolt(TM) Configuration > Discrete Thunderbolt(TM) Support option is enabled.
Step 2.2: (For THUNDERBOLTEX_4 card) Enable Thunderbolt function
Make sure the THUNDERBOLTEX_4 card is connected to the motherboard.
Access the BIOS setup and ensure that the Advanced > Thunderbolt(TM) Configuration > Discrete Thunderbolt(TM) Support option is enabled.
Step 3: Run the FW update tool
1. Extract the XXX_TBT_FW_31_V1.4 file and copy Shell.efi to a USB drive.
2. Insert the USB drive into the motherboard.
3. Press the [Power key] and then hold [F2] to enter the BIOS setup menu.
4. If the BIOS setup is in [EZ mode], press [F7] to switch to [Advanced mode].
5. Select [Exit] and choose [Launch EFI Shell from USB drive] to enter the shell mode for the update process.
Step 4: Downgrade to TBT NVM31
Follow the instructions provided by the tool. Please note that the downgrade process may take some time, so be patient until it is completed.
Step 5: Check for compatibility issues
After the FW downgrade is completed, restart your system and reconnect your Thunderbolt devices. Keep in mind that downgrading to an older FW version may result in known compatibility issues.
Please be aware that downgrading FW carries certain risks and may cause other issues or limit functionality. Prior to proceeding with the downgrade, ensure that you understand and accept these risks.

Thunderbolt 1/2 devices will no longer be supported after this FW update due to a change made by intel regarding the update of Thunderbolt firmware to NVM 36.