The doc you mentioned should be fine: docs.iredmail.org/subdomain.web.apps.html

Thanks for confirming Zhang,
I am busy with prepping the proposed config for the solution,
I will revert with an update once I have implemented,
Thank you for following up as well, much appreciated.

Hello Community,

Require your expert assistance/guidance on best approach in separating iRedMail Pro admin domain cert and an existing email domain already using the same cert,
The prod email domain cert is fully functional with its own cert, which I want to avoid breaking.
Attempting to now separate the administration portal cert as this currently presents the mail domain cert and not the admin domain cert (this has not been setup by previous admin so I guess its the expected behavior), considering iredadmin.tmpl is part of the nginx default config here: 00-default-ssl.conf

My instance hosted in Azure, the IP associated is issued by azure, the associated DNS is also created by azure default x.x.cloudapp.azure.com, the x.x.cloudapp.azure.com/iredadmin/ FQDN is reached via the same associated IP for the mail domain.
I am considering creating a separate admin FQDN using letsencrypt or to use the existing azure assigned FQDN leveraging Letsencrypt to request a standalone SSL certificate for my Azure domain, however taking best practice into consideration and if the Community has a standard approach in similar scenario's, I am open to reviewing this as well.
I have reviewed a few articles online e.g. docs.iredmail.org/subdomain.web.apps.html and researched a few options, however would cautiously prefer to validate options/solutions with an experienced professional before attempting this on my end and inadvertently breaking anything.

Your expert assistance/guidance on this matter is really appreciated,

Thank you.