Ploi makes it a breeze to run Laravel Horizon. You can use the 'Daemons' tab in server level to configure this.
Use this command to run Laravel Horizon:
php /home/ploi/my-app.com/artisan horizon, 1 process is enough as Laravel Horizon is able to spawn multiple supervisor workers. (More at the Laravel Documentation)
Take the following screenshot as an example:
This will spawn a supervisor configuration file like this:
command=php /home/ploi/my-app.com/artisan horizon