• Activate odoo developer
• Go to the bug on the view
• Edit view on control panel
• Add:

<search string="Search Opportunities">
                    <field name="name" string="Opportunity" filter_domain="[                         '|', '|', '|', '|',                         ('partner_id', 'ilike', self),                         ('partner_name', 'ilike', self),                         ('email_from', 'ilike', self),                         ('name', 'ilike', self),                         ('contact_name', 'ilike', self)]"/>
                    <field name="partner_id" operator="child_of" string="Customer" filter_domain="[                         '|', '|', '|',                         ('partner_id', 'ilike', self),                         ('partner_name', 'ilike', self),                         ('email_from', 'ilike', self),                         ('contact_name', 'ilike', self)]"/>
                    <field name="tag_ids" string="Tag" filter_domain="[('tag_ids', 'ilike', self)]"/>
                    <field name="user_id"/>
                    <field name="team_id"/>
                    <field name="stage_id" domain="[]"/>
                    <field name="country_id"/>
                    <field name="city"/>
                    <field name="phone_mobile_search"/>
                    <field name="activity_state"/>
                    <field name="sequence_name"/>

• https://www.odoo.com/ru_RU/forum/pomoshch-1/how-do-i-search-for-custom-fields-in-the-search-bar-of-a-view-or-tree-table-144377