Question about registering a behavior

[bancroftway]

I have a question regarding correct way to register my behavior whose complete code is below.

I have tried this way, but the behavior does not get called:

 builder.Services.AddMediatR(cfg => {
     cfg.RegisterServicesFromAssemblies(typeof(Program).Assembly);
     cfg.AddBehavior<IPipelineBehavior<IAppRequest<BaseResponse>,BaseResponse>, UnhandledExceptionBehavior<IAppRequest<BaseResponse>, BaseResponse>>();
 });

public class UnhandledExceptionBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IAppRequest<TResponse>
    where TResponse : BaseResponse
{
    private readonly ILogger<UnhandledExceptionBehavior<TRequest, TResponse>> _logger;

    public UnhandledExceptionBehavior(ILogger<UnhandledExceptionBehavior<TRequest, TResponse>> logger)
    {
        _logger = logger;
    }

    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
    {
        try
        {
            return await next();
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Unhandled Exception for Request {Name} {@Request}", typeof(TRequest).Name, request);

            var response = Activator.CreateInstance<TResponse>();
            response.IsSuccess = false;
            response.ErrorMessage = $"An error occurred while processing your request: {ex.Message}";

            return response;
        }
    }