Put this in your platformio.ini file and it should work:
[env:giga_r1_m7]
platform = GitHub - dberlin/platform-ststm32: ST STM32: development platform for PlatformIO
board = giga_r1_m7
framework = arduino
platform_packages = platformio/framework-arduino-mbed@^4.1.5
;tool-dfuutil@~1.9