Our .NET 5 RPM requires an existing .NET 5 SDK to build. So far, we have been putting a prebuilt SDK into the "source" tarball. We should fix that and use the existing packaged .NET 5 SDK and keep our source tarball free of prebuilts.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Important: .NET 5.0 on RHEL 7 security and bugfix update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2021:3818