Can you check that you are not using the RUI2 code base with the RUI1 online compiler?
RUI2 git GitHub - RAKWireless/Products_practice_based_on_RUI_v2.0
RUI2 online compiler: https://build.rakwireless.com/
RUI1 git GitHub - RAKWireless/Products_practice_based_on_RUI: This repository will collect all of products practice based on RAK IoT module and RAK IoT SDK RUI.The creativity may come from RAK official and open source contributor.
RUI1 online compiler http://22.214.171.124:12090/#/user/login
Just checked both and the compile is done normally.
Yes, the error is explaining what is missing
Try this rak811.zip