[Python] Set default value for date field in portal odoo18

In Odoo18, I created template for a portal user which inherit another template, In my custom template, I want a date fields 'birthday' to be auto filled

<t t-set="last_app" t-value="request.env['hr.applicant'].search([ ('partner_id', '=', partner.id), '|', ('active', '=', False), ('active', '=', True)], order='id desc', limit=1)"/>
<xpath expr="//input[@name='birthday']" position="replace">
<input id="birthday_input"
type="text"
name="birthday"
class="form-control o_website_form_date"
t-att-value="last_app.birthday and last_app.birthday.strftime('%Y-%m-%d') or ''"
data-date-format="yyyy-mm-dd"
required="required"
placeholder="YYYY-MM-DD"/>
</xpath>


but I still got a wrong value 01/01/1970

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