There's still some things being worked out, see the ESP32 section at the top of the README on GitHub. Biggest issue is probably dealing with memory management on the ESP32. When adding other libraries to the project, e.g. SD or WiFi, memory issues can lead to the other libraries not working, or getting into a rolling reboot situation. Moving matrix.begin() later in the sketch, so the SmartMatrix mallocs are the last things called is a decent workaround for now.