How to get MENDER_DATA_PART_GROWFS=y to work using mender convert?

We read that MENDER_DATA_PART_GROWFS=y would expand /data partition to fill up rest of the sdcard at first boot, just like normal raspios images do. Is there something more than setting this flag in mender convert needed to get the data partition to expand at first boot? How is the expansion done? By some service via config that we can verify in the device? Can we verify it is enabled at convert time?