After uploading a new build last night, I received this email:
We identified one or more issues with a recent delivery for your app, "Super Dungeon Delvers" 0.916 (0.916). Your delivery was successful, but you may wish to correct the following issues in your next delivery:
ITMS-90809: Deprecated API Usage - Apple will stop accepting submissions of apps that use UIWebView APIs . See developer.apple.com/documentation/uikit/uiwebview for more information.
After you’ve corrected the issues, you can use Xcode or Application Loader to upload a new binary to App Store Connect.
The App Store Team'
I can't see anything in the link that states when the submissions will be stopped, but I'm hoping this is not going to be an issue moving forward.