sbs_diasymreader.dll

This DLL is part of the .NET Framework.

• sbs - side by side (Recall - allows multiple versions of a DLL to sit side-by-side without conflicts)
• dia - Debug Interface Access, reference to SDK used to read debugging symbols (PDB files)

In Windows 11, it sits in C:\WINDOWS\Microsoft.NET\Framework along with other sbs_xxx DLLs.