Dear ZinggJM,
could you tell us more how to use 2.9inch Waveshare display with Arduino Nano/Uno. Let's leave 5V-3.3V voltage conversion issues.
I don't know pin assignments and library usage:/
I tried to figure out pinout shown in i.e. GxGDEH029A1.cpp file but it is for DESTM32-S2 connection board for STM32 system not for Arduino:/
Please put some light how to talk to WaveShare e-papers from Arduino.
One of the problems i found during compilation is that variable used to store screen resolution is uint8_t. 2.9inch screen has 296 x 128 pixels so 296 is greater that uint8_t can handle so overflow errors appeard. This is just one of the errors.