Downloading ISOs from unofficial forums or "free" mirrors poses a high risk of malware or pre-installed backdoors.
It sounds like you're looking for a specific version of the Windows 10 ISO file.
Available for active Visual Studio (formerly MSDN) subscribers.
: If you have an active subscription, you can sign in to the Visual Studio portal to download legacy ISOs, including 21H2. Alternative Reliable Sources Internet Archive
If you're looking to download the Windows 10 21H2 ISO file, you can do so from the official Microsoft website. Here's how:
: Modern systems with more than 4GB of RAM require the 64-bit (x64) version to utilize all available memory.