Link to BennVenn’s shopify:
https://bennvenn.myshopify.com/collections/flash-carts/products/elcheaposd-v2-2-xmas-special
Some reference sources to look into:
http://www.loirak.com/gameboy/gbprog.php
https://www.jrodrigo.net/wiki/how-to-diy-a-gameboy-flash-cartridge-with-a-rom-adapter-board/
Try also replace the gbc screen with a back light. There are tutorials available and hardware can be found online.