Windows 7 requires Microsoft's official SHA-2 security update before .NET 4.8 can be installed:
Step 1: Install Microsoft SHA-2 Update (KB4474419)
Double-click to install the update, then restart your computer.
Step 2: Install .NET Framework 4.8 Standalone
Run this installer once your PC restarts.
Step 3: Run R1Soft Setup
Click "Download for Windows (setup.exe)" above to complete installation.