Hello Rostyslav Sulym,
You can add filed in search view by adding your field in new view which must be inherited from the existing search view.
<record id="sale_order_view_search_inherit_quotation" model="ir.ui.view">
<field name="name">sale.order.search.inherit.quotation</field>
<field name="model">sale.order</field>
<field name="mode">primary</field>
<field name="inherit_id" ref="sale.view_sales_order_filter"/>
<field name="arch" type="xml">
<xpath expr="//filter[@name='my_sale_orders_filter']" position="after">
<field name="your_field_name" />
<field name="your_field_name" />
<separator />
<field name="your_field_name" />
</xpath>
</field>
</record>