I installed this Microsoft.Extensions.Configuration.Binder package and the problem solved. The strange thing is that when I was using .net-core3.1 I did not need to install it from Nuget but after updating to .net5 I needed to install this package separately.
I solved the problem by installing the Hosting bundle from here.
While the other answers are good and solves the problem, if all you want is the general behavior to be like pre netcore3, you can use the Microsoft.AspNetCore.Mvc.NewtonsoftJson NuGet package and in Startup.cs do: services.AddControllers().AddNewtonsoftJson() More info here. This way, you don’t need to create any extra json-converters.
I found the cause of this error could be multiple things in your code. For me at least, the best way was to add verbose in command. With that will be able to understand what is the problem. the verbose will display all steps of the execution. In visual studio use: add-migration Added_something -verbose For … Read more