According to this article: https://doc.arcgis.com/en/appstudio/create-apps/licenseappstudio.htm you need Qt SDK license if you wish to charge users for your app, or if you want to include C++ extensions and advanced tools. There is also written this:
"In some cases, the licenses are free but still require you to acknowledge the use of different components".
And I would like to know in what cases are licenses free (I assue this is open source version of Qt SDK) and in what case I have to buy Qt SDK license.
And I have quite the same question about using ArcGIS runtime for Qt. Do I need a commercial Qt license or can I use LGPL version of Qt?