[2022-07-22 17:07:29] local.WARNING: json_decode(): Passing null to parameter #1 ($json) of type string is deprecated in /XXX/XXXX/XXX/XXX/myapp/vendor/laravel/horizon/src/Http/Controllers/FailedJobsController.php on line 122  
(As my deprecation log was set to a null driver I got an exception for this on top.)
[2022-07-21 14:15:28] laravel.EMERGENCY: Unable to create configured logger. Using emergency logger. {"exception":"[object] (InvalidArgumentException(code: 0): Log [deprecations] is not defined. at /XXX/vendor/laravel/framework/src/Illuminate/Log/LogManager.php:207)
Visiting the Horizon dashboard under "'/horizon/failed" will produce this warning in the deprecation log file.

It looks like the value of $job->retried_by is just an empty array [] which leads to this warning which multiples by the amount of failed jobs.
Steps To Reproduce:
My Job is just a generic one to experiment with:
class DebugJob implements ShouldQueue
    use Dispatchable, InteractsWithQueue, Queueable, SerializesModels;
    public $tries = 2;
    public $backoff = [3, 5, 6]; //  sec 
    public Domain $domain;
    public function __construct(Domain $domain)
        $this->domain = $domain;
    public function handle()
        $ip = Ip::inRandomOrder()->first();
        logger("DebugJob ++++ STARTED... for IP: {$ip->id}");
        if (random_int(1,5) >= 2)
            throw new \Exception("DebugJob ++++ FAILED ... for IP: {$ip->id}");
        logger("DebugJob ++++ FINISHED ... for IP: {$ip->id}");
config/queues.php
        'redis' => [
            'driver' => 'redis',
            'connection' => 'default',
            'queue' => env('REDIS_QUEUE', 'default'),
            'retry_after' => 10,
            'block_for' => null,
            'after_commit' => false,
horizon.php
    'defaults' => [
        'supervisor-1' => [
            'connection' => 'redis',
            'queue' => ['setup','email','default'],
            'balance' => 'auto',
            'maxProcesses' => 50,
            'maxTime' => 0,
            'maxJobs' => 0,
            'memory' => 512,
            'tries' => 3, // DEFAULT can be overwritten in Job
            'timeout' => 360,
            'nice' => 0,
EDIT FIX:
It's basically this PHP 8.1 issue: laravel/framework#41643
Changing FailedJobsController.php#L122

FROM:

$job->retried_by = collect(json_decode($job->retried_by))

$job->retried_by = collect(json_decode((string)$job->retried_by))
If it's correct, let me know I will push a PR.
Deprecation log get blown up with json_decode() warnings
[PHP 8.1] Deprecation message from json_decode in FailedJobsController
    Jul 23, 2022