Declare FormArray for multi-checkbox

                  itemArray: FormArray;
                  

add itemArray to mainform group

                  this.mainForm = this.fb.group({
                      'id': [''],
                      'name': ['', Validators.required],
                      
                       itemArray: this.fb.array([ ])
                  
                  });
                  

Define itemArray structure

                  createItem(item:any): FormGroup {
        
                      return this.fb.group({        
                          id:[item.id],
                          title:[item.title],
                          isChecked: [item.isChecked]          
                        
                      });
                
                  }
                  

populate data to checkbox

1) Access 'itemArray' controls of mainForm Group

                  this.items = this.mainForm.get('itemArray') as FormArray;
                  

2. push the value to itemArray

                  this.permissions.forEach(row => {                            
                     this.items.push(this.createItem(row));
                   });
                   

1) Note, this.permissions is json data
2) this.permissions contains, [{id:1,title:'sun',isChecked:true}, {id:2,title:'mon',isChecked:true}]
3) variable 'row' is passed to this.createItem() for setting value

                    <label>Permissions<span style="color:red;">*</span></label>
                    <div class="form-group row" > 
                          <div class="col-sm-4" *ngFor="let row of mainForm.get('itemArray')?.controls;let index = index;">
                              <span style="float:left;position:relative;"><input type="checkbox" class="form-control" [formControl]="row.get('isChecked')"  style="width:18px;"></span>
                              <span style="float:left;position:relative;top:8px;">&nbsp;{row.get('title').value}</span>
                          </div>
                    </div> 


                  

Note that 'itemArray' control is looped, mainForm.get('itemArray')?.controls;