bank-statement-import/account_bank_statement_clear_partner/views/account_bank_statement_views.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2020 Tecnativa - João Marques
     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->

<odoo>
    <record id="view_bank_statement_form" model="ir.ui.view">
        <field name="model">account.bank.statement</field>
        <field name="inherit_id" ref="account.view_bank_statement_form"></field>
        <field name="arch" type="xml">
            <button name="%(account.action_bank_reconcile_bank_statements)d" position="after">
                <button name="clear_partners" string="Clear partners" type="object" class="oe_highlight" attrs="{'invisible':['|','|',('all_lines_reconciled','=',True),('line_ids','=',[]),('state', '!=', 'open')]}"/>
            </button>
        </field>
    </record>
</odoo>