This issue has been fixed.

On November 26, 2019, Vernier Software & Technology released an updated version (4.0.6) of Graphical GW to resolve issues related to iOS 13.

Nevertheless, we recommend users of Graphical Analysis GW switch to the modern Graphical Analysis 4 app if GW is not required.

Graphical Analysis 4 is available here:
https://itunes.apple.com/us/app/vernier-graphical-analysis-4/id1385963326?mt=8

For details about why there are two apps, and when you might still choose to use Graphical GW, see What is the difference between Graphical Analysis app (Graphical) and Graphical Analysis GW (GraphicalGW)?