Advantech's office asked for $500 for optimizing the firmware for the LCD matrix NL10276BC20-04. To do this, they ask to send them to Taiwan my matrix, motherboard and all connecting cables.
However, I was able to successfully modify the firmware myself.
For this I used the Chrontel CH7511B Utility, and some instructions on how to use them, which were not easy to obtain.
The task is quite simple, it was enough for me to correct only 2 DTD parameters: HB (Hor. Blanking) and VB (Ver. Blanking), which are calculated using the factory specifications of the LCD matrix presented in
Datasheet according to the formula : HB = Hsync Period - Hsync Active; VB = Vsync Period - Vsync Active. And also the clock frequency (DCLK) has been slightly adjusted and the size of the visible area.
Thus, the LCD matrix now works perfectly. As you can see in the attached photos, now the image scaling occurs correctly, both in DOS mode and after loading Windows.
Perhaps it will be useful to someone else in the future, so I am attaching to the letter my firmware optimized for the NL10276BC20-04 matrix (Lec1.bin):
https://drive.google.com/file/d/1pVnBnOJF5OahTJMiuA6iCdQS9HPOywiH/view?usp=sharing