Why Does My Phone Fail to Flash Stock Firmware in Download Mode?

Summary: I am unable to revert my Samsung Galaxy Note 9 or **N9600** (Snapdragon variant) to stock firmware due to an issue where Download Mode doesn’t allow flashing, and I’m receiving error messages during the flashing attempts. When I try to enter Download Mode, I only see a blue screen with a downloading icon, and no information is displayed, unlike the usual mode where information such as "Do Not Turn Off Target" is shown. I disabled the OEM Unlock option, thinking it was the culprit and that doing so would fix the errors I encountered with Odin. Unfortunately, this only made things worse, as now I’m seeing the "Custom Binary (boot) blocked by OEM Lock" message, preventing my device from booting properly. --- What happened: 1. OEM Unlocking: OEM Unlock was enabled, but I disabled it, and after a reboot, the "Custom Binary (boot) blocked by OEM Lock" message appeared, making the phone unbootable and showing the error when starting. 2. Download Mode Issue: I’ve tried using Odin to flash the stock ROM multiple times, but it fails. When I attempt to use the SamFirm tool, I get an "**MTP Fail**" message. 3. Recovery Mode: In the past, I flashed TWRP (custom recovery) for the "crownqltechn" variant from this forum: https://xdaforums.com/t/official-twrp-sm-n9600-galaxy-note-9-crownqltechn.3845536/ and installed DotOS. To remove TWRP, I flashed the stock recovery image, believing it would help resolve issues with the bootloader. Now, I have the stock Android recovery instead of TWRP. 4. Download Mode Behavior: When choosing “Reboot to Bootloader” in recovery mode, it opens Download Mode, but it looks different from when I press Bixby + Volume Down. The usual information doesn’t show up (e.g., “Do not turn off target”). It only shows the blue screen with the downloading icon. --- What I tried: Used multiple stock ROMs from different sources (SamFirm, etc.), placed the correct files in Odin as usual, but received errors during flashing. The error messages I encountered include:

threads completed, succeeded 0 / failed 1.

Additionally, I tried changing various Odin options (like "Flash Lock" and "NAND Erase"), but they made no difference. Odin just can't deliver anything to Android while in this abnormal Download Mode. However, the phone is still recognized by Odin, and the blue box appears. Tried the ADB sideload option in the stock recovery options, but realized it’s only meant for applying software updates, and I couldn't use ADB commands either (e.g., adb getprop). The phone was in sideload mode when using the "Apply Update" option from Recovery. Downloaded and installed the latest Samsung drivers (version 1.7.61.0) to ensure proper communication between my phone and the PC, but the issue persists. --- Current Status: OEM Unlock is disabled, and I can’t access Developer Options or the OS because of the "OEM Lock" message upon boot. --- Additional Info from DM: >CURRENT BINARY: Custom > >FRP Lock : OFF > >OEM LOCK : ON > >KG STATUS : Checking > >RP SWREV : B9(1,1,1,9,1) K9 S9 Other details from Download Mode include RPMB and DID. I really don't plan to use closed-source and paid software; I just want to see what options I have.