Garmin sends that data to an Intervals.icu web hook endpoint. I don’t know how Garmin decides when to send new data.
You can download old wellness data from the Garmin box in /settings. But be careful with that one. Garmin restrict backfill calls heavily. The don’t allow repeat calls for the same dates etc.. Garmin sends the data to the webhook endpoint asynchronously making all of this a bit of a pain.