I downloaded the .exe installer from download.qt.io but it asks me to login to continue to install. I recall there is a skip button on the installation window to bypass the login in the past Qt releases. Does not Qt 5.12.11 allow to install without an account? I disconnect the network connection but the skip button never appears.
B.T.W, more and more software/website require you to register to use their service. Is there some philosophy behind this trend? At the first glance, this policy creates inconvenience thus reduces potential users.
You could dowload the offline installer, the online installer require a qt account. Offline installer link.
First you should download and install the qt creator and then download and install the qt source package, if you do not want to use the qt-creator then you do not have to dowload that.