Nobody is forcing you to use their IDE. Just use VSCode.
Also, for your complaint about the size of the SDK: most people download the Python bindings (often through conda) and don't do compilation at all (I write interactive applications using QtPy, python slowness isn't an issue). But also: you're not the target audience.
That is besides the point parent poster is making though. are they also making it so that you cannot use the GPL software w/o the IDE? if so that would be a violation of GPL.
But i'm also really not that interested in using a library specific IDE at that level.
Because QT is not all i do, etc.
For folks who do, i'm sure it's great.
For C++ IDEs on linux, CLion works great. VSCode is reasonable too.