Microsoft provide a comprehensive guide to various methods of finding out what version of .NET is installed on your PC or server:  https://docs.microsoft.com/en-us/dotnet/framework/migration-guide/how-to-determine-which-versions-are-installed?redirectedfrom=MSDN#net_d

Probably the most accessible method is as follows:

• Open the Registry Editor
• Locate this subkey:  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full
• The Release entry contains a six digit value:
  
  

(in this case, the value is 528049)

• Check the value against the table at: Determine which .NET Framework versions are installed - .NET Framework | Microsoft Learn:
  
  
  
  
• In this example, we see that the installed version (528049) is at or after 528040 and is lower than 533325, so the installed version is 4.8