Hello,
Yes. You do need to implement those functions and use the library. LVGL needs to be there as a whole to generate the widgets/images/buttons, whatever you add based on a design you have made. Luckily for you, the ILI9488 is quite popular and people have already written flush (and probably read) functions for it:
for instance: Ili9488 & lvgl?
There are probably more on the Internet.
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