I’ve added support and created a pull request into the main PlatformIO repo.
Can you remove your
C:\Users\heikk\.platformio\packages\framework-arduino-mbedC:\Users\heikk\.platformio\platforms\nordicnrf52
folders and use the platformio.ini in Add Xiao nRF52840 (Sense) board support by maxgerhardt · Pull Request #151 · platformio/platform-nordicnrf52 · GitHub?
Note that Git should be installed for this to work.