The .NET Framework 4.8.1 (KB5011048) is available for download from: Download .NET Framework Free official downloads (microsoft.com) for supported versions of Windows and is also included with Visual Studio 17.3 and Windows 11 22H2, and their corresponding newer versions.
Whilst the above answers are correct its worth noting that MSBuild has changed and it no longer ships with the .net framework, it comes either stand alone or with visual studio. As a result it's binaries have moved... so the one you get under the 4.0.303619 directory is actually the old one!
I've just been caught out by this - I found automatic binding redirects were only working when running from VisualStudio but not when running msbuild from the command line... the clue was that binding redirects were added in VS 2013 (for that read .net framework 4.5). If you open up a vs command prompt you'll see it now gets it from program files as the other article mentions. Whereas I was using a batch file on my path which linked to the old version.
I was trying to test our products to make sure that they are compatible with Windows Server 2016. And during some testing, I mistakenly thought that I can simply "downgrade" .NET framework from 4.6 to 4. So I removed .NET 4.6 from Roles and from IIS.
A cross-platform and open-source framework, .NET Core is best when developing applications on any platform. .NET Core is used for cloud applications or refactoring large enterprise applications into microservices.