Qt 5.15.2 offline installers are no longer provided for open-source users. Starting with Qt 5.15, the Qt Company restricted offline installers and long-term support (LTS) binaries to commercial license holders
Starting with , The Qt Company discontinued offline installers download qt 5.15.2 offline installer
https://download.qt.io/archive/qt/5.15/5.15.2/qt-opensource-linux-x64-5.15.2.run which you can reuse offline.
After installation, ensure your PATH variable includes the bin folder of your Qt installation (e.g., C:\Qt\5.15.2\msvc2019_64\bin ). This allows your system to find qmake and the necessary DLLs. download qt 5.15.2 offline installer
This downloads all components into ./qt_cache , which you can reuse offline.