does openmv use the m4 core? if not, can it be programmed with Arduino while using openmv?
No it’s not used, you can enable it manually omv/boards/PORTENTA/omv_boardconfig.mk here by setting: OMV_ENABLE_CM4=1 and add your code here: cm4/src/main.c, rebuild, and flash the two images (CM4, CM7). However, you should keep the default code if you need to use the low-power standby mode.