Since Epic won't give you one officially, you have to become the archivist of your own engine version. Here is the professional workflow to create a true offline backup of UE 4.27 (the last great version before UE5 took over).
The Catch: Understanding Official vs. Third-Party Installers
: Paste this folder onto your offline PC. You can run the editor directly without the launcher by navigating to Engine\Binaries\Win64\UnrealEditor.exe (or UE4Editor.exe for older versions).
The Epic Games Launcher is the standard tool for downloading Unreal Engine 4 (UE4). However, it relies heavily on a stable, high-speed internet connection. If you have limited bandwidth, strict firewall restrictions, or need to deploy the engine across multiple laboratory computers, the standard launcher can fail you.