When you try to install the .NET Framework on Windows 7, the error description may be: NET Framework 4.8 has not been installed because:
A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider.

Solution:

To resolve this issue, you must download and install the KB4474419 update

- Download from the Microsoft site

- Download from our x64 server

- Download from our x32 server

After installing the updates, restart your PC and try to reinstall the .NET Framework.