Add the following to the bottom of Boards.txt in the Arduino>hardware>expressiv>esp32

##############################################################

m5cam.name=M5 Camera

m5cam.upload.tool=esptool
m5cam.upload.maximum_size=1310720
m5cam.upload.maximum_data_size=294912
m5cam.upload.wait_for_upload_port=true

m5cam.serial.disableDTR=true
m5cam.serial.disableRTS=true

m5cam.build.mcu=esp32
m5cam.build.core=esp32
m5cam.build.variant=m5cam
m5cam.build.board=M5CAM

m5cam.build.f_cpu=240000000L
m5cam.build.flash_mode=dio
m5cam.build.flash_size=4MB
m5cam.build.boot=dio
m5cam.build.partitions=default

m5cam.menu.FlashFreq.80=80MHz
m5cam.menu.FlashFreq.80.build.flash_freq=80m
m5cam.menu.FlashFreq.40=40MHz
m5cam.menu.FlashFreq.40.build.flash_freq=40m

m5cam.menu.PartitionScheme.default=Default
m5cam.menu.PartitionScheme.default.build.partitions=default
m5cam.menu.PartitionScheme.no_ota=No OTA (Large APP)
m5cam.menu.PartitionScheme.no_ota.build.partitions=no_ota
m5cam.menu.PartitionScheme.no_ota.upload.maximum_size=2097152
m5cam.menu.PartitionScheme.min_spiffs=Minimal SPIFFS (Large APPS with OTA)
m5cam.menu.PartitionScheme.min_spiffs.build.partitions=min_spiffs
m5cam.menu.PartitionScheme.min_spiffs.upload.maximum_size=1966080

m5cam.menu.UploadSpeed.921600=921600
m5cam.menu.UploadSpeed.921600.upload.speed=921600
m5cam.menu.UploadSpeed.115200=115200
m5cam.menu.UploadSpeed.115200.upload.speed=115200
m5cam.menu.UploadSpeed.256000.windows=256000
m5cam.menu.UploadSpeed.256000.upload.speed=256000
m5cam.menu.UploadSpeed.230400.windows.upload.speed=256000
m5cam.menu.UploadSpeed.230400=230400
m5cam.menu.UploadSpeed.230400.upload.speed=230400
m5cam.menu.UploadSpeed.460800.linux=460800
m5cam.menu.UploadSpeed.460800.macosx=460800
m5cam.menu.UploadSpeed.460800.upload.speed=460800
m5cam.menu.UploadSpeed.512000.windows=512000
m5cam.menu.UploadSpeed.512000.upload.speed=512000

Clone the folder varients>esp32 and rename to M5Cam

and change

static const uint8_t SDA = 21;
static const uint8_t SCL = 22;

to

static const uint8_t SDA = 12;
static const uint8_t SCL = 13;

recompile and upload and it should now detect any i2c devices connected to the grove connector.