Step 1: Just delete this file:
C:\Program Files (x86)\Microsoft SQL Server Management Studio 18\Common7\IDE\CommonExtensions\Platform\Microsoft.VisualStudio.MinShell.Interop.pkgdef
Alternatively, rename the file so it does not have the .pkgdef extension.
Step 2: Optionally, you can remove the following Windows Registry Key (created at SSMS 18 startup using the .pkgdef file mentioned above):
HKEY_CURRENT_USER\SOFTWARE\Microsoft\SQL Server Management Studio\18.0_IsoShell_Config\RuntimeConfiguration\dependentAssembly\bindingRedirection\{8BC7AF31-B6DA-4B97-8B36-F0500DECB147}