Restrict entries to specific users
If you are faced with such a task, then I think it's better to use user IDs, getting from the method a ids from the field in which users are stored, and check the received array using the in method. Another option is a plugin https://plugins.craftcms.com/user-group-field.
 {% set usersIds = entry.usersField.ids %} 

    {% if currentUser.id in usersIds %} 
        Show the page
    {% else %}
        Permission Denied
    {% endif %}