I'm not aware of a front-end way to set a default, but you can use a SQL query to copy from your "template" contact to new users as you create them. Below is an example:

insert into civicrm_dashboard_contact (
    dashboard_id,
    contact_id,
    column_no,
    is_minimized,
    is_fullscreen,
    is_active,
    weight,
    content,
    created_date)
select
    dashboard_id,
    35, -- replace with new contact id
    column_no,
    is_minimized,
    is_fullscreen,
    is_active,
    weight,
    content,
    NOW()
from
    civicrm_dashboard_contact 
where 
    contact_id = 1 -- replace with contact id whose dashboard you want to copy
;

If you use a certain contact type/group/tag to define back office users, you can join to the appropriate table and do it all at once rather than one contact at a time.

I'm not aware of a front-end way to set a default, but you can use a SQL query to copy the dashboard setup from your "template" contact to new users as you create them. Below is an example:

insert into civicrm_dashboard_contact (
    dashboard_id,
    contact_id,
    column_no,
    is_minimized,
    is_fullscreen,
    is_active,
    weight,
    content,
    created_date)
select
    dashboard_id,
    35, -- replace with new contact id
    column_no,
    is_minimized,
    is_fullscreen,
    is_active,
    weight,
    content,
    NOW()
from
    civicrm_dashboard_contact 
where 
    contact_id = 1 -- replace with contact id whose dashboard you want to copy
;

If you use a certain contact type/group/tag to define back office users, you can join to the appropriate table and do it all at once rather than one contact at a time.