Currently, I am using this function: Answer bot -  transfer to agents, however, I can't find every agent's workload in the report.

There is no updater/agent can be added to the metric in Messaging channel, I don't want to add assignee though because I don't think this can give me the exact data to measure how many tickets each agent replies because this agent might not reply to the tickets but being assigned only. I hope you can add a Updater/Agent in the metric field for Messaging channel so that I can inspect every agent's real workload.