Hi, there are already several articles, describing all kinds of ways to sync, see:
https://forum.intervals.icu/search?q=sync%20weight
If you’re okay with running a python script on a machine I have a solution that get’s the data directly from the Withings API and pushes it straight to the Intervals.icu API - see Weight tracking (Intervals, Strava, Wahoo) - #12 by rolandplanitz