contract/contract/security/contract_security.xml

<odoo noupdate="1">
    <record id="rule_contract_contract_multi_company" model="ir.rule">
        <field name="name">Contract contract multi-company</field>
        <field name="model_id" ref="model_contract_contract" />
        <field name="global" eval="True" />
        <field
            name="domain_force"
        >['|', ('company_id', '=', False), ('company_id', 'child_of', [user.company_id.id])]</field>
    </record>
    <record id="rule_contract_line_multi_company" model="ir.rule">
        <field name="name">Contract line multi-company</field>
        <field name="model_id" ref="model_contract_line" />
        <field name="global" eval="True" />
        <field
            name="domain_force"
        >['|', ('contract_id.company_id', '=', False), ('contract_id.company_id', 'child_of', [user.company_id.id])]</field>
    </record>
    <record id="rule_contract_template_multi_company" model="ir.rule">
        <field name="name">Contract template multi-company</field>
        <field name="model_id" ref="model_contract_template" />
        <field name="global" eval="True" />
        <field
            name="domain_force"
        >['|', ('company_id', '=', False), ('company_id', 'child_of', [user.company_id.id])]</field>
    </record>
    <record id="rule_contract_template_line_multi_company" model="ir.rule">
        <field name="name">Contract template line multi-company</field>
        <field name="model_id" ref="model_contract_template_line" />
        <field name="global" eval="True" />
        <field
            name="domain_force"
        >['|', ('contract_id.company_id', '=', False), ('contract_id.company_id', 'child_of', [user.company_id.id])]</field>
    </record>
</odoo>