I’m glad to hear that the examples are working for the OLED.
I suggest getting the SD card working first before reloading the bin file as well as diving into the DaisyGranular code.
In terms of learning C++, I recommend starting out with the DaisyDuino. The resources/tutorials for Arduino IDE (which uses C++) will come in handy when you start using .cpp with Daisy. General learning-materials for .cpp, like C++ textbooks, can go way too deep and cover topics that are unnecessary for using the Daisy. After you get comfortable programming in Arduino IDE, you can perhaps start looking into the code for the DaisyGranular.
That being said, it may be quite an undertaking if you’re just getting start with text-based programming. Instead, it could be better for you to keep using that new granular synth (Grnltr - A Granulator on the Daisy Pod ) which I saw you trying out (so SD Card is working for you??). And it could be more fun to customize that code to your liking.
To clarify and summarize the main issue of this topic…
The problem is that the firmware files for DaisyGranular were compiled prior to libDaisy adding support for the rev5 daisy seed. Since there are sources, you can try to rebuild it on a newer version of libDaisy.