Not sure what am I doing wrong.
This worked on earlier odoo versions.

<field name="context">{'search_default_groupby_partner': 1}</field>

Takes no effect, full view code bolow

<odoo>

    <record id="board_invoice_tree" model="ir.ui.view">
        <field name="name">Invoices</field>
        <field name="model">account.invoice</field>
        <field name="arch" type="xml">
            <tree default_order="date_invoice desc">
                <field name="partner_id"/>
                <field name="date_invoice"/>
                <field name="number"/>
                <field name="user_id"/>
                <field name="amount_total_company_signed"/>
                <field name="state"/>
            </tree>
        </field>
    </record>

    <record id="board_invoice_search" model="ir.ui.view">
        <field name="name">board_invoice_search</field>
        <field name="model">account.invoice</field>
        <field name="arch" type="xml">
            <search string="Search">
                <group expand="1" string="Group By">
                    <filter string="Partner" name="groupby_partner" domain="[]" context="{'group_by': 'partner_id'}"/>
                </group>
            </search>
        </field>
    </record>

    <record id="board_invoice_action" model="ir.actions.act_window">
        <field name="name">Invoices</field>
        <field name="res_model">account.invoice</field>
        <field name="view_type">form</field>
        <field name="view_mode">tree</field>
        <field name="view_id" ref="board_invoice_tree"/>
        <field name="search_view_id" ref="board_invoice_search"/>
        <field name="domain">[('state', 'in', ['open', 'paid']), ('type', '=', 'out_invoice')]</field>
        <field name="context">{'search_default_groupby_partner': 1}</field>
    </record>

    <record id="maco_board_view" model="ir.ui.view">
        <field name="name">Maco Board</field>
        <field name="model">board.board</field>
        <field name="arch" type="xml">
            <form>
                <board style="1-1">
                    <column>
                        <action name="%(board_invoice_action)d" string="Invoices"/>
                    </column>
                    <column>

                    </column>
                </board>
            </form>
        </field>
    </record>

    <record id="maco_board_action" model="ir.actions.act_window">
        <field name="name">Maco Board</field>
        <field name="res_model">board.board</field>
        <field name="view_type">form</field>
        <field name="view_mode">form</field>
        <field name="view_id" ref="maco_board_view"/>
    </record>

    <menuitem id="maco_board_menu" parent="base.menu_board_root" action="maco_board_action" sequence="1"/>

</odoo>