How do I save my interface as a picture?

I want to convert my interface into a picture and save it to a USB disk. How should I do that?

As of 8.1 (not released yet), LVGL has a native feature for taking snapshots in the LVGL image format. You should be able to convert that to a BMP with minimal effort if you use LV_IMG_CF_TRUE_COLOR_ALPHA as the format.