Only you know how to blind flash that system? I thought you said you already did once before?

To blind flash, you have to have flashed from DOS or BIOS before, and know by heart of have written down the exact keystrokes from poweron/startup, to do the same now, but without seeing the screen.
Or, have a second same exact machine, prepare BIOS flash on USB, power on system, make note of each and every keystroke you make to flash BIOS, then do exact same on system with graphics disabled.

To use autoexec batch file, you have to know this system can flash BIOS by DOS, prepare the BIOS file and bootable USB with autoexec and flash tool on it, and then power on system and hit exact keystrokes you need to hit to get to DOS
Really, almost impossible to do any of this, unless you planned in advanced and know or have written down the keystrokes, or have a second same system right beside you.
But, autoexec has good chance, if you just need to hit "Boot Menu" hotkey, then one keystroke down to USB then enter, if fail reboot and try again with two down and enter, then three down and enter etc until you find it

@Lost_N_BIOS
I hate AFU too but when I have emergency I have to use AFU.

See my edits above. I would leave it, get a flash programmer, then fix it properly, before I'd use AFU

@Lost_N_BIOS
Can you tell me which autoexec.bat command does fix the Asus black screen?

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@Lost_N_BIOS
I have to use because I don't want to open my laptop unless it cannot power on. I don't want to use SPI Programmer.

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@Lost_N_BIOS
Please answer me!

@XPWELL64 - please stop making multiple posts in a row if no one has replied, if you need to add more info, questions, thoughts etc and no one replied yet please use the edit button on right side of your post.
Additionally, demanding that I answer you isn't going to help me answer you any faster, nor is bumping your thread (that actually puts you lower on my reply list, since I try to start with older posts I haven't replied to yet)

To answer you, sorry, I do not know with any certainty what command line you put into autoexec.bat, nor what AFU DOS version works for this system, only you can know that from past experience or finding in google etc.
Once you find compatible AFU then you make DOS Bootable USB, put AFU and BIOS file on there, along with Autoexec.bat that contains this line >> AFUDOS.exe nameofbios.rom /P /B / N /X /Shutdown

SPI programmer may be your only option

@Lost_N_BIOS
I used HP Usb Disk storage format tool with modified autoexec bat only contains afudos.exe nameofbios.rom /P /B /N /X /Shutdown. I formatted my usb and created a dos usb. I copied my bios as nameofbios.rom. I copied afudos and tried every combination. What's the wrong step during the recovery process?
Here is my boot order before I bricked it:
1- Optical Drive - CD/DVD drive
2- UEFI USB
3- Legacy HDD (I installed legacy windows on it)
4- Legacy USB
5- Enter setup

What you need to do is find another user here, and have him write down each keystroke to flash BIOS normal method, then you do same blindly.
How do you know that is your boot order shown on the "Boot Menu" screen, surely you couldn't remember that.

Anyway, if the above is 100% true. Then what you do is have USB ready in USB port. Turn on system and wait a second or two then hit whatever hotkey is your "boot Menu" hotkey, then press down arrow three times to get legacy USB, then wait for it to reboot after flash.

Confirm your USB/Autoexec setup works, put on another system and edit autoexec to run backup instead (afu backup.bin /O) and then boot to USB on another AMI system and see if it makes backup. If so, then you know your setup is correct.

Also, if above is true, you should be able to do the following. Boot system, wait a few seconds, hit boot menu hotkey, then press down key four times to enter BIOS, then press F5, then enter, then F10 (System should reboot, this loads optimal defaults and saves/exits)

@Lost_N_BIOS
At first, I only changed igpu setting F9 is the only solution. At second, I changed muxed-muxless option and igpu setting. Muxed-Muxless option does not give black screen but after changine igpu, it gave black screen and F9 isn't a solution anymore.

I don't know what "F9" is? And, it doesn't matter what you changed, if you reload optimal defaults then all settings made previously will be gone, same as if you reflash BIOS

I tried it 100 times and it was unsuccessful.

Did you order CH341A + SCI8 test clip with cable yet? If not, order now, the longer you wait to order the longer it will take to arrive.
Meantime, search around forum and find user with same system, ask them to test flash stock BIOS with whatever version DOS AFU (NOT old one with /GAN)
Once they confirm it flashes OK, then ask them to redo, making a note about each keystroke from startup to finish

What did you try 100 times??? If you mean blind flash, or BIOS reset, keep trying, sounds like you are not hitting perfect key combo (especially for BIOS entry and load of optimal defaults)

You also never answered me, did you test all external display connections? Sometimes external will get a display output when this happens, not always, but sometimes.

@Lost_N_BIOS
The first question's answer is NO. I will never open inside the laptop. The second question's answer is BIOS reset. I'm using the hacked one with /GAN. I used HDMI output on my TV. It was unsuccessful. I never used VGA output before on my laptop.

Longer you wait to order, the longer you wait to fix it. Then you may have to throw it away if you refuse to open laptop, or set it in closet and cover with clothes
Up to you, opening it may be your only option, unless you can still RMA and want to pay to ship it out.

BIOS Reset, as I mentioned, you may not be hitting the right key strokes, or at right time to be where you think you are in BIOS.

There is no "Hacked One" w/ GAN. That is a VERY old Leaked Engineer version for BIOS three series ago and over 10+ years ago, not for this system, it may work, sometimes to force in a mod BIOS, or it may brick BIOS even worse even if it was working at the time
Two things additionally, those versions do not support encapsulated BIOS, which your system uses. And, this kind of AFU is ONLY needed when you are trying to force flash a modified BIOS, never needed for stock BIOS, and is always a risk to make a brick itself
So, summary, DO NOT use that

You need to use V4 or probably V5 AFU versions, BIOS is Aptio V

Try VGA, it's not about what you used or tried in the past. Connect a monitor or display to all possible display outputs and see if you can see anything on screen while booting up.
Connect it before you turn the system on, and wait a good 2-3 minutes at each time you test this.

@Lost_N_BIOS
The USB and keyboard were detected. Here are three photos for the evidence:

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@Lost_N_BIOS
Look at this photos.

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@Lost_N_BIOS
Please look at these photos.

Yes, that shows power to USB, this does not mean anything in regards to BIOS recover possibilities (not all models can recover by USB)
If this one can you should find info / how-to on google, I am not familiar with all possible recovery methods for laptops you'll have to look in google for Asus laptop BIOS recovery and or your model and BIOS recovery etc)

Please stop making multiple posts in a row to bump your thread!