Example = build WFLY, boot it and access console:
Runtime->default=serverIO->worker=default

It will show x of x Threads with '100% Used' on idle server. Since explanation is vague in https://docs.wildfly.org/29/wildscribe/subsystem/io/worker/index.html I cant be sure what it show - how users could?
If its just total number, than Utilization is not a UI object that should be used.
If its free threads/resources - 100% Used on idle does not sound right.