template_id = 11 # lookup not working with env.ref('mail.template.Envoi dem. collocation, CV et CC (SRH)').id
compose_form_id = env.ref('mail.email_compose_message_wizard_form').id

attachment = {
  'name': str(record.x_studio_cv_filename),
  'datas': record.x_studio_cv,
  'res_model': 'mail.compose.message',
  'type': 'binary'
}

cv = env['ir.attachment'].sudo().create(attachment)

cdc_record_id = record.x_studio_contrat.x_studio_many2one_field_KdGBT.id
# studio_customization.studio_report_docume_f5a65386-780e-43d0-b161-8a7e54ebcc8a
cdc_report = env.ref('studio_customization.cahier_des_charges_r_7fd43d12-8c21-42f0-a93b-ed8e6a84e543')
cdc_pdf = cdc_report._render_qweb_pdf(cdc_record_id)
# cdc_pdf = env['report'].sudo().get_pdf([cdc_record_id], 'studio_customization.studio_report_docume_f5a65386-780e-43d0-b161-8a7e54ebcc8a')
cdc = env['ir.attachment'].create({
    'name': 'Cahier des charges.pdf',
    'type': 'binary',
    'raw': cdc_pdf[0],
    'res_model': 'x_cahier_des_charges',
    'res_id': cdc_record_id,
    'mimetype': 'application/x-pdf'
})

ctx = {
'default_model': 'x_engagement_chercheur',
'default_res_id': record.id,
'default_use_template': bool(template_id),
'default_template_id': template_id,
'default_composition_mode': 'mass_mail',
'default_attachment_ids': [cv.id, cdc.id]
}

action = {
'type': 'ir.actions.act_window',
'view_type': 'form',
'view_mode': 'form',
'res_model': 'mail.compose.message',
'views': [(compose_form_id, 'form')],
'views_id': compose_form_id,
'target': 'new',
'context': ctx,
}