Do Post-EOS Windows Server 2008 R2 patches also apply to Small Business Server 2011?

SBS 2011 reached end of support in January 2020, but Microsoft extended their support for Exchange 2010 and SharePoint 2010 (part of SBS 2011) to October 2020 (source), and you should keep applying their updates.

SBS 2011 is based on Windows Server 2008 R2, and according to our tests, binaries that are present on both are identical. This means that micropatches for Windows Server 2008 R2, updated with January 2020 updates, should automatically apply to an equally fully-updated SBS 2011.

However, while we're providing security micropatches for issues Microsoft is fixing with Windows Server 2008 R2 Extended Security Updates, we are not providing security micropatches for issues that may only affect SBS 2011 (specifically Exchange and SharePoint), so it can happen that some component of SBS 2011 is not covered with our micropatches.

In summary, our coverage of SBS 2011 is likely incomplete so if you're concerned about the security of Exchange or SharePoint on your SBS 2011, 0patch probably does not adequately meet your needs.