IMO Qt is amazing. No login is technically required to download anything, especially code.

The official SDK installer GUI does require a login, but you don't have to use it in order to download or use Qt at all.

Not only can you download all the individual components that the GUI fetches via download.qt.io yourself, there's also third-party installers like aqtinstall, as well as many different OS package managers that provide Qt binaries.