We may observe that the Service Contact Center Agents are receiving Voice Calls even if they are having 100% capacity. It is an expected behavior since Salesforce Voice Call work item have higher priority over the other Service Channel Work Items.

Since Salesforce phone voice calls have a higher priority than work items from other Service Channels, the capacity limit setup in the Presence Configuration will not affect the Phone Service Channel. So, the voice calls are routed to agents regardless of their work capacity. In the Omni-Supervisor, we will see the capacity is at more than 100% since the Voice Calls are routed.

Following option or feature will help to resolve this issue:

Respect Agent Capacity

Currently, Respect Agent Capacity feature is in Beta.

Reference Article:
https://help.salesforce.com/s/articleView?id=000390654&type=1