The hiding of an application to a user is dependent upon who or if it’s been assigned to the user or not. Application assignment can be done individually or to a group. If the user is a member of the group they will be assigned the application and it will be present on their Okta dashboard. The group can be one from AD/LDAP or and application group like Office 365 or a Google group, or it can be an Okta mastered group.
Once a user is removed from the group, or the application is unassigned from the user individually the icon will be hidden/removed from the users dashboard.