Using the installer means adhering to the open-source tracks:
Due to Qt’s changed distribution policies, you cannot find qt-opensource-windows-x86-5.15.2.exe on the official Qt Download page for new users. However, it remains available: qt-opensource-windows-x86-5.15.2.exe
You can launch the installer with a mirror parameter in a command prompt or terminal: Using the installer means adhering to the open-source