before v18
<group expand="0" string="Group By">
    <filter string="Employees" name="employee_id" context="{'group_by':'employee_id'}"/>
    <filter string="Manager"   name="manager_id" context="{'group_by':'manager_id'}"/>
    <filter string="Loan type" name="type"       context="{'group_by':'loan_type_id'}"/>
    <filter string="States"    name="state"      context="{'group_by':'state'}"/>
</group>


after v19
<group>
    <filter string="Employees" name="group_emp"   context="{'group_by': 'employee_id'}"/>
    <filter string="Manager"   name="group_mgr"   context="{'group_by': 'manager_id'}"/>
    <filter string="Loan type" name="group_ltype" context="{'group_by': 'loan_type_id'}"/>
    <filter string="States"    name="group_state" context="{'group_by': 'state'}"/>
</group>


If you want a visual divider/label inside the dropdown, add a separator (it’s allowed to have a string):


<separator string="Group By"/>
<group> … </group>

In v19 the menu already has “Group By”, so this is mostly cosmetic.)
To set a default grouping, use the list view’s default_group_by attribute (not the search view), e.g. on your <tree>:

<tree default_group_by="employee_id"> … </tree>



this is an Odoo 19 change. In search views, the <group> element no longer accepts attributes like expand or string. That’s why <group expand="0" string="Group By"> errors in v19. 

Hi,

Please refer to the code:

<group>

    <filter string="Employees" name="employee_id" context="{'group_by':'employee_id'}"/>

    <filter string="Manager" name="manager_id" context="{'group_by':'manager_id'}"/>

    <filter string="Loan type" name="type" context="{'group_by':'loan_type_id'}"/>

    <filter string="States" name="state" context="{'group_by':'state'}"/>

</group>

Hope it helps.