I downloaded the .NET Framework 4.8 and 4.8.1 Runtime Offline installers from the links below.
It seems strange that 4.8.1 is significantly smaller (by 44 Megabytes).
.Net Framework 4.8.1 = 77 Mbs .Net Framework 4.8 = 121 Mbs
Were some libraries or something else eliminated in the 4.8.1 release vs 4.8?
I checked a blog article "Announcing .NET Framework 4.8.1" and did not see any mention of deletions. https://devblogs.microsoft.com/dotnet/announcing-dotnet-framework-481/
Download .NET Framework 4.8 https://dotnet.microsoft.com/en-us/download/dotnet-framework/net48
Download .NET Framework 4.8.1 https://dotnet.microsoft.com/en-us/download/dotnet-framework/net481
@mamift answered in comment above "One reason could be because 4.8.1 drops support for older Windows versions. 4.8 supported Windows 7, 8, and Windows 10 versions prior to 2020H2, while 4.8.1 doesn't: devblogs.microsoft.com/dotnet/announcing-the-net-framework-4-8"
Accepting that answer and marking this question closed.