why old browser is not support reactive form disabled in angular code example

Example 1: how to set disabled flag formgroup angular

this.form.controls['name'].disable();

// or

<input formControlName="id" placeholder="ID" [attr.disabled]="true"></input>

Example 2: form control adding disabled and validators

value: string;
isDisabled: boolean;
//isDisabled and value come from your dynamic data.  
fb: FormBuilder;
myGroup: FormGroup;

this.myGroup = fb.group({
   form_control_name: new FormControl({
      value: this.value,
      disabled: this.isDisabled,
      Validators.required)}
   );