I am currently using Alma + CP and faced the DKIM signature error issue.
I ended up hiring a Linux expert and he solved the problem.
Below I will transcribe what he pointed out to me as an error.
“It was also necessary to configure OpenDKIM, it had incorrect permissions, I believe this is a CyberPanel bug.”
So it could probably be a bug in the Cyber Panel itself, if the developers can see that!