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ASP.NET Core - Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions'

After upgrading some packages in an ASP.NET Core application, I got the following error message when I tried to run the application:

System.TypeLoadException: Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly 'Microsoft.AspNetCore.Mvc.Formatters.Json, Version=3.1.20.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'.

   at System.Signature.GetSignature(Void* pCorSig, Int32 cCorSig, RuntimeFieldHandleInternal fieldHandle, IRuntimeMethodInfo methodHandle, RuntimeType declaringType)

   at System.Reflection.RuntimeConstructorInfo.get_Signature()

   at System.Reflection.RuntimeConstructorInfo.GetParametersNoCopy()

   at System.Reflection.RuntimeConstructorInfo.GetParameters()

   at Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)

   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.<>c__DisplayClass4_0.<UseMiddleware>b__0(RequestDelegate next)

   at Microsoft.AspNetCore.Builder.ApplicationBuilder.Build()

   at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)

This issue was caused because I was using a newer Microsoft.AspNetCore.Mvc package together with an older Swashbuckle package. To solve the problem I had to update Swagger to version 5:

<PackageReference Include="Swashbuckle.AspNetCore" Version="5.0.0" />
That’s it!
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