Only warn instead of an exception

src/NCronJob/Scheduler/QueueWorker.LogMessage.cs

@@ -39,4 +39,7 @@ internal sealed partial class QueueWorker
 
     [LoggerMessage(LogLevel.Information, "Job removed from queue: {JobType} at {RunAt}")]
     private partial void LogJobRemovedFromQueue(string jobType, DateTime? runAt);
+
+    [LoggerMessage(LogLevel.Warning, "The UseNCronJob(Async) method was not called. Startup jobs did might not be executed.")]
+    private partial void LogUseNCronJobNotCalled();
 }

src/NCronJob/Scheduler/QueueWorker.cs

@@ -124,10 +124,7 @@ private void AssertUseNCronJobWasCalled()
     {
         if (!missingMethodCalledHandler.UseWasCalled)
         {
-            throw new InvalidOperationException("""
-                                                UseNCronJob(Async) was not called on the host.
-                                                Make sure to call app.UseNCronJob() (or await app.UseNCronJobAsync()) in your Program.cs.
-                                                """);
+            LogUseNCronJobNotCalled();
         }
     }