hello @26.albertsilva@gmail.com,
edp-dp converter is not supported on tinker 3n, the edp connectors can only be used for the edp display panels that are on the qvl: https://tinker-board.asus.com/download/Tinker_Board_3N_QVL.pdf
to test out dual screen setup, here i use a hdmi tv and an 15" auo g156hab02 edp panel, with tinker 3n debian 11 image v.1.0.7:
modify /boot/config.txt, uncomment the overlay line, save /boot/config.txt and reboot tinker 3n:
once the overlay comes effective and the edp is recognised, you can change it to either primary or secondary display in the display settings: