I was doing it on surface go, and what’s missing is wintab drivers – they are not installed by default by microsoft.
You can get them for example from this download https://www.microsoft.com/en-us/download/details.aspx?id=49498 – pick wintab file (32 or 64 bit version, depending on your OS). Don’t worry that this download is for surface 4 – it’s generic software that just sets up stuff needed for older software to work.
After installing it, the alpha started working correctly! The drawing lag is pretty large though (at least on go) – hopefully gets fixed.
Would be nice to have this in installation notes, or to support modern api!