repeater ID How it work?

@bigimatt14 You can try simplifying the code itself…

let daRimuovere = [];
   $w("#repeater1").onItemReady(($item, itemData, index) => {
        $item("#btnAdd").onClick((event) => {
            console.log('clicked');
            boxId = index;
            daRimuovere.push(boxId);
             $item('#btnAdd').enable;    
      });
    });
            

Or you can follow your code, but with little modifications…

$w("#repeater1").onItemReady(($item, itemData, index) => {
        $item("#btnAdd").onClick((event) => {
            console.log('clicked');
            boxId = index;
            daRimuovere.push(boxId);
            enableButton();
    });
  });
                     
         
     function enableButton () {
       $w("#repeater1").forItems(daRimuovere, ($item, itemData, index) => {
        $item('#btnAdd').enable;
    });
  }