The policy regarding offline installers changed starting with Qt 5.15.
Local copies of the entire API reference, which allows for coding without searching online documentation. Qt6 Offline Installer
A: For open-source (LGPL/GPL), yes—as long as you do not charge for it and you preserve the original licensing notices. For commercial, check your Qt license agreement; redistribution is usually permitted within your organization. check your Qt license agreement
The offline installer supports a scripted mode: Qt6 Offline Installer