<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="payment_method_is_active">
        <observer name="disable_payment" instance="MagemonkeysDisablePaymentObserverPaymentMethodAvailable" />
    </event>
</config>

<?php
namespace MagemonkeysDisablePaymentObserver;
use MagentoFrameworkEventObserverInterface;
class PaymentMethodAvailable implements ObserverInterface
{
    public function execute(MagentoFrameworkEventObserver $observer)
    {
        // you can replace "checkmo" with your required payment method code
        if($observer->getEvent()->getMethodInstance()->getCode()=="checkmo"){
            $checkResult = $observer->getEvent()->getResult();
            $checkResult->setData('is_available', false); 
        }
    }
}