'lv_demo_widgets' was not declared in this scope

I installed the lvgl 8.3 library in the arduino ide,
copied the examples and demos directories into the src directory,
in the lv_config file I set #define LV_USE_DEMO_WIDGETS to 1,
in the LVGL_Arduino.ino wall I uncommented lv_demo_widgets(); from row.
However, ‘lv_demo_widgets’ was not declared in this scope
I get an error message.