Select all checkboxes in RecyclerView

You made a simple mistake here

  if (!isSelectedAll) holder.select_item.setChecked(false);
    else holder.select_item.setChecked(true);

change setSelected into setChecked thats it

for both Select All and Unselect All

activty

 checkall.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(checkall.isChecked()){
                categoryAdapter.selectAll();
            }
            else {
                categoryAdapter.unselectall();
            }


        }
    });

in adapter

  public void selectAll(){
        isSelectedAll=true;
        notifyDataSetChanged();
    }
    public void unselectall(){
        isSelectedAll=false;
        notifyDataSetChanged();
    }



    @Override
    public void onBindViewHolder(@NonNull final MyviewHolder holder, int position) {
        final CategoryListItems list = categoryListItems.get(position);
        holder.text.setText(list.getName());
        if (!isSelectedAll){
            holder.checkbox.setChecked(false);
        }
        else  holder.checkbox.setChecked(true);