Impact of expired certificates on servers?

Please provide real life examples of what goes wrong when a certificate expires on a server.

I get that the end user might see browser errors, data is moved around in plaintext, or the desktop application might not work well with the OS (or maybe none of those things are true).

Just looking for some direction and clearer understanding of why this is a security risk.

application browser certificate certificates cybersecurity data desktop desktop application end end user errors expired expired certificates impact life plaintext real life examples server servers things work wrong