services.Configure<FormOptions>(options =>
 {
              
                options.MultipartBodyLengthLimit = 50000;
 });

services.AddRazorPages(options =>
            {
                options.Conventions.AddPageApplicationModelConvention("/FileUploadPage",
                   model => { 
                       model.Filters.Add(new RequestSizeLimitAttribute(5000)); 
                   });

            }).AddRazorRuntimeCompilation()

@attribute [RequestSizeLimitAttribute(50000)]