How to filter users that have a custom field set?

We want to set automation rules using a User custom field. I understand we have to setup the user with this field and select an option. But how do you know what Users have this field set?

I want to set a rule that when a ticket is created to use this Initial support custom field to notify a group of users. But I know how to set this in each user, but I want to create a list of who has each option set?

I don't see a column for a filter by to see this custom field: