How to bind default value in mat-radio-group angular reactive forms

What you want to do is to remove the checked and instead set the preselected value to your formControl, so when you build your form:

constructor(private fb: FormBuilder) { 
  this.myForm = this.fb.group({
    options: ['1']
  })
}

and then you just remove the checked attribute:

<mat-radio-group formControlName="options">
  <mat-radio-button value="1">Option 01</mat-radio-button>
  <mat-radio-button  value="2">Option 02</mat-radio-button>
</mat-radio-group>