That’s no reason the checkout was down, check system log error about Braintree payment gateway
and we found the Solution https://community.magento.com/t5/Magento-2-x-Technical-Issues/Braintree-Error-in-Magento-2-4/m-p/460018#M15891
php bin/magento module:status
If module is enable then disable by below command:
php bin/magento module:disable
php bin/magento setup:di:compile
