Paper checks are no longer sent to the Fed for processing, they are imaged and uploaded to the fed, the actual check is shredded after a time it is held. Most imaging is done in a bank branch, if you are sending checks to a payment center the USPS could be a delay, sorting at the payment center and processing time. Many people are still WFH but checks cannot leave the payment center so they are being imaged and staff that is WFH is processing than submitting to the Fed.
Using online billpay from your bank eliminates the payment center step and is super secure. I use it for paying bills that require the bank to send a paper check, saves on postage and hassles mailing.