Starting with , the Qt Company changed its distribution model, making official offline installers available exclusively for commercial license holders
On the 5.15.2 page, you will see multiple subdirectories. Here is what matters:
If you must have an offline setup, you can download the source code and build it yourself. The source packages (tar.xz or .zip) are available in the official archive . Third-Party & Alternative Methods Install Qt creator 5.15.2 - Qt Forum
Click the link to download. File sizes are large (~2-3 GB), so this may take time depending on your connection.