That's quite an ambiguous area of the LGPL. Qt is a C++ app so linking it with the `.o` files from your app is going to be extremely difficult. I'm not sure it would qualify for the LGPL and anyone who says it is is frankly just guessing. The language is not clear and it has never been tested in court (and probably won't ever be).

I certainly wouldn't base a business on that risky interpretation, and the one business that I have been in that used the LGPL version of Qt dynamically linked it. It's just less risky (plus you don't need to build it yourself then).