@csaba911 You can't expect QtCompany to provide official Qt installers/binaries for every existing and future platform/hardware. This is simply not possible because of limited resources and time.
If you want to do cross compilation, then yes you have to learn how it works, this is life.
Did you check https://wiki.qt.io/Raspberry_Pi_Beginners_Guide ?
"Linux and Qt is so discouraging to use it, I don't understand people and their mind" - then don't use it, really...
I use both since many many years and don't want to use anything other than Linux for software development.
Posts like yours do not improve anything, sorry. Constructive critic, improvement suggestions and patches are welcome (this is how open source works).