The Qt Installer Framework (QTIFW) is part of the Qt Framework which is available under the LGPL3. This page lists the components that are available under each license. Unfortunately it doesn't list QTIFW but if you download the open source version of Qt you can install it so presumably it is available under the LGPL3.
So next the question is, can I package closed source software into a binary installer if the license of the installer source code is LGPL3? Does packaging a program in an installer make it a 'Combined Work'? The LGPL3 mainly talks about linking with libraries, not bundling in installers.
Is there an official position from The Qt Company about this?
According to this comment (not from a Qt employee) there is an exception in the license that does allow including a closed source program that is dynamically linked with Qt inside a QTIFW installer (that is statically linked with Qt). However there is no specific license for QTIFW in the Qt installer so it is presumably licensed the same as Qt (GPL3 or LGPL3) and I can't find any relevant exceptions.
When I downloaded the old QTIFW 1.3 it did present a Digia Qt LGPL Exception Version 1.1 license with the following text:
Digia Qt LGPL Exception version 1.1
As an additional permission to the GNU Lesser General Public License version 2.1, the object code form of a "work that uses the Library" may incorporate material from a header file that is part of the Library. You may distribute such object code under terms of your choice, provided that:
(i) the header files of the Library have not been modified; and
(ii) the incorporated material is limited to numerical parameters, data structure layouts, accessors, macros, inline functions and templates; and
(iii) you comply with the terms of Section 6 of the GNU Lesser General Public License version 2.1.
Moreover, you may apply this exception to a modified version of the Library, provided that such modification does not involve copying material from the Library into the modified Library's header files unless such material is limited to (i) numerical parameters; (ii) data structure layouts; (iii) accessors; and (iv) small macros, templates and inline functions of five lines or less in length.
Furthermore, you are not required to apply this additional permission to a modified version of the Library.
However it seems this exception is a) only applicable to the LGPL2.1, b) no longer used, and c) not really relevant here.