Why is AWS Certificate Manager not required to enter 443 settings when deploying?

Question

I know that there are let's encrypt and ACM for the certificate method.

I'm currently deploying with Nginx and certified with ACM. After issuing an SSL certificate with ACM, I created a record in Route 53 and set up an EC2 Load Balancer.

But why is the following code required when SSL certificate is issued with let's encryp, whereas is not needed when SSL certificate is issued with ACM?

server {
listen 443 ssl;
ssl_certificate "/etc/letsencrypt/live/rtcworld.xyz/fullchain.pem";
ssl_certificate_key "/etc/letsencrypt/live/rtcworld.xyz/privkey.pem";
}