If you want to apply conditional validation on 'Middle Name' or 'Last Name', then you need to add 'First Name' input as 'Bharat'
{{userForm.controls?.firstName?.errors?.required.message}}
Conditional Required Validation.
Conditional validation will be applied if the 'FirstName' field have value of 'Bharat'
Conditional Expression with type 'string'
{{userForm.controls?.lastName?.errors?.required.message}}
Shows Custom Validation Message.
{{userForm.controls?.userName?.errors?.required.message}}