According to the compatibility list and the release notes for the latest version v1.1.4, it seems that ArduinoGraphics does not work with GIGA, so I think the only way is to use LVGL when you display something on the GIGA Display Shield.
I recommend that you first configure LVGL, then run the examples in "GIGA Display Shield LVGL Guide" or LVGLDemo example in Arduino_H7_Video, in order to become familiar with LVGL.