I have had to correct this too many times already. Server is the name of the deployment type of their on-prem. It means single node non-clustered. Data center is their deployment that supports clustering to multiple nodes (and used to support a few extra features). They are retiring the Server deployment type licenses and pushing everyone to data center or cloud. So no, they aren’t EOLing their on-prem.
The datacenter product also seems geared towards people reselling Atlassian stacks. For example there's a company that offers HIPAA compliant Confluence (complete with signing a BAA, so you can actual store PHI on it). It doesn't seem like a great replacement for the server version.
