@Louis, see SmartMatrix/src/SmartMatrixAPA102RefreshEsp32_Impl.h at teensylc · pixelmatix/SmartMatrix · GitHub
this seems wrong in an Esp32_Impl file.
@GeorgeFlorian you are however getting this error in SmartMatrix_Impl.h which shows that you are likely using the master branch which does not support ESP32, instead of the teensylc branch which does support ESP32.