If the CodeBuild failed with following issue:
 

Err:4 https://deb.nodesource.com/node_14.x focal Release
  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  
Could not handshake: Error in the certificate verification. 

 
Try to add the following command before installing the node in your buildspec.yml file:
 

- apt-get update
- echo Installing Certificate...
- apt-get install ca-certificates

 
References:
https://github.com/nodesource/distributions/issues/1266