Yup looks like postfix is not even trying to send email to opendkim for adding signature although by the looks of it the configs of postfix seems fine.
Normally when postfix connects to opendkim it is like
root@cyberpanel:~# journalctl -f | grep dkim
Jan 10 10:49:17 cyberpanel.net opendkim[579]: 3447740AAD: DKIM-Signature field added (s=default, d=wpmautic.net)
and postfix logs are like this if it cant connect to opendkim → Message not signed with DKIM - #14 by lesupremo
If you have CP add-ons then either reset mail configs it may solve the issue or try reaching our support as I can not see anything wrong.