Can good display 7.5 b/w/r change image at runtime?

There is something wrong if you get Busy Timeout. Do you use the suggested wiring? Else you need to change the values in the constructor for your display.

Adafruit_GFX is in Arduino/libraries, else the example would not compile.

You need to select the 3-color display GDEW075Z09 according your first post.

GxEPD2_32_3C display(GxEPD2::GDEW075Z09,  /*CS=5*/ SS, /*DC=*/ 17, /*RST=*/ 16, /*BUSY=*/ 4);

In this part of the example you can find direct drawing to controller buffer and/or screen:

#ifdef _GxBitmaps200x200_H_
void drawBitmaps200x200()
{
  const unsigned char* bitmaps[] =
  {
    logo200x200, first200x200, second200x200, third200x200, fourth200x200, fifth200x200, sixth200x200, senventh200x200, eighth200x200
  };
  if (display.panel() == GxEPD2::GDEP015OC1)
  {
     // ...
  }
  else
  {
    bool mirror_y = (display.panel() != GxEPD2::GDE0213B1);
    display.clearScreen(0xFF);
    uint16_t x = (display.width() - 200) / 2;
    uint16_t y = (display.height() - 200) / 2;
    for (uint16_t i = 0; i < sizeof(bitmaps) / sizeof(char*); i++)
    {
      display.drawImage(bitmaps[i], x, y, 200, 200, false, mirror_y, true);
      delay(2000);
    }
  }
  bool mirror_y = (display.panel() != GxEPD2::GDE0213B1);
  for (uint16_t i = 0; i < sizeof(bitmaps) / sizeof(char*); i++)
  {
    int16_t x = -60;
    int16_t y = -60;
    for (uint16_t j = 0; j < 10; j++)
    {
      display.writeScreenBuffer(0xFF);
      display.writeImage(bitmaps[i], x, y, 200, 200, false, mirror_y, true);
      display.refresh();
      delay(2000);
      x += 40;
      y += 40;
      if ((x >= display.width()) || (y >= display.height())) break;
    }
    break; // comment out for full show
  }
  display.writeScreenBuffer(0xFF);
  display.writeImage(bitmaps[0], 0, 0, 200, 200, false, mirror_y, true);
  display.writeImage(bitmaps[0], display.width() - 200, display.height() - 200, 200, 200, false, mirror_y, true);
  display.refresh();
  delay(2000);
}
#endif

For bitmap in RAM set the last parameter to false.