It's available under LGPL v3 and GPL v2 <https://www.qt.io/product/features> so it is free to use in both commercial and non-commercial programs, you don't need to provide the source code of your program as long as Qt is dynamically linked, meaning that you should keep the DLLs out of your program's binary.
> In case of dynamic linking, it is possible, but not mandatory, to keep > application source code proprietary as long as it is “work that uses the > library” – typically achieved via dynamic linking of the library. In case of > static linking of the library, the application itself may no longer be “work > that uses the library” and thus become subject to LGPL. It is recommended to > either link dynamically, or provide the application source code to the user > under LGPL. <https://www.qt.io/licensing/open-source-lgpl-obligations>
