Please find code here :-
Using the create method:
class Applicant(models.Model):
_inherit = "hr.applicant"

@api.model_create_multi
def create(self, vals_list):
records = super(Applicant, self).create(vals_list)
for record in records:
partner_names = self.env['hr.applicant'].search([('partner_name', 'ilike', record.partner_name), ('active', 'in', [True, False])]).mapped('partner_name')
if len(partner_names) > 1:
raise UserError('You Cannot Create the Same Applicant')
return records

Hello Jainesh,

This is great, thank you!
The only adjustment we need to make is that the client should be able to create applications with the same applicants name, as two people can share the same name. How do we make the user aware of a potential duplicate upon creation, but still let them create it if necessary (remove the blocker of UserError)?

Kind regards,
Tord Røsstad