Qt 5.6 and later switched from LGPL v2.1 to v3. The main difference is the addition of the anti-tivoization clause that the regular GPLv3 has, wherein you cannot sell hardware that integrated Qt without providing a way for the user to replace your copy of the libraries with their own. Although at that point most people just buy a commercial license, and I think the majority of people that complain about this don't have a legitimate use-case that really affects them as much as they lead on.

Mostly, 5.x broke many dependencies due to how the linking impacted license compliance issues. This meant users would be left to figure out why several features were turned off in the Debian package built.

I prefer wxwidgets, as its lgpl style license allows static-linking on both open or closed projects without submarine-IP-fees... undeniably useful when cross-porting to some platforms.

We may have differing opinions, as our use-cases likely differ. =3

but both Qt and WX is LGPL ?

wxwidgets is a slightly more permissive license than lgpl.

When people must static link on some closed mystery object, than the subtle difference becomes very important.

lgpl works great in the Linux .so design paradigm, but it can cause problems on rare occasion for porting. =3