Hi,

Your code will hide for all users except admins but you need to add is_admin field to kanban view to be able to use it in domains.

<xpath expr="//field[@name='activity_state']" position="after">

<field name='is_admin' invisible="1"/>

</xpath>

If it's not work try the below please try the below: 

You can create a security group and it will be disabled for all users except root and admins and you can give access to users individually.  

<record id="view_progress_bar" model="res.groups">
<field name="name">View Progress bar</field>
<!-- Add super user and admin to group, you can delete the below line to hide for them as well --> 
<field name="users" eval="[(4, ref('base.user_root')), (4, ref('base.user_admin'))]"/>

</record>


Then inherit view and add the below:

<xpath expr="//progressbar[@field='activity_state']" position="attributes">
<attribute name="groups">[YOUR_Module_Name].view_progress_bar</attribute>
</xpath>

Then and for each user you want to view the progress bar, you will enable developer mode then go Settings -> users -> open required user

Edit the user record and you will see at the bottom your create group with Checkbox named "View Progress bar" and you will check it to allow user to view progress bar.

Please up vote if this help.