Fix code

app/Console/Kernel.php

@@ -48,7 +48,7 @@ class Kernel extends ConsoleKernel
     protected function schedule(Schedule $schedule): void
     {
         $schedule->call(
-            static function () {
+            static function (): void {
                 app('log')->error(
                     'Firefly III no longer users the Laravel scheduler to do cron jobs! Please read the instructions at https://docs.firefly-iii.org/'
                 );