Since BlueStacks officially pushes the latest version (currently 5.21+), you cannot find 5.9.300 on their main homepage.

Users with Hyper-V enabled may need specific Admin privileges to launch the app. Fastest & Lightest Android App Player for PC - BlueStacks 5

For weeks, his favorite mobile battle royale had been stuttering on his aging PC. He had heard whispers in the forums that version 5.9.300 was the "Golden Build"—the one with the perfect balance of RAM optimization and frame-rate stability. He navigated to the official BlueStacks download page