For those like me who’ve never used QT: As long as you don’t statically link the QT libraries you don’t have to open source your entire commercial application. I’m not a lawyer.
“(1) If you statically link against an LGPL'd library, you must also provide your application in an object (not necessarily source) format, so that a user has the opportunity to modify the library and relink the application.”
So for LGPL. As a commercial application developer I’m not sure I’d want to do that. I’d then have to field support requests for that object file.
I provided a link from the FSF that shows that this is not the case just below - you can statically link proprietary apps with LGPL qt.