If you're building this filter in the XML of the search view or using the search domain directly in code (e.g., Python or JS), you must explicitly structure the domain with an AND condition like:
[('birthdate', '>=', start_date), ('birthdate', '<=', end_date)]

Hi Mr Tessa
check this 

<!-- Define a custom search view with proper date range filters -->
<record id="view_your_model_search" model="ir.ui.view">
    <field name="name">your.model.search</field>
    <field name="model">your.model</field>
    <field name="arch" type="xml">
        <search string="Search Records">
            <field name="name"/>
            <field name="birthdate"/>
            
            <!-- Custom date range filter -->
            <filter name="birthdate_range" string="Birth Date Range" 
                    domain="[]" 
                    context="{'search_default_birthdate_range': 1}"/>
            
            <!-- Predefined date ranges -->
            <separator/>
            <filter name="born_this_year" string="Born This Year"
                    domain="[('birthdate', '>=', context_today().strftime('%Y-01-01')),
                             ('birthdate', '<=', context_today().strftime('%Y-12-31'))]"/>
            
            <filter name="born_last_year" string="Born Last Year"
                    domain="[('birthdate', '>=', (context_today() - relativedelta(years=1)).strftime('%Y-01-01')),
                             ('birthdate', '<=', (context_today() - relativedelta(years=1)).strftime('%Y-12-31'))]"/>
            
            <group expand="0" string="Group By">
                <filter string="Birth Month" name="group_birth_month"
                        context="{'group_by': 'birthdate:month'}"/>
                <filter string="Birth Year" name="group_birth_year"
                        context="{'group_by': 'birthdate:year'}"/>
            </group>
        </search>
    </field>
</record>