<input class="popup-uploadImage__input" value=""/>
<button class="popup-uploadImage__button--delete off">delete</button>
<button class="popup-uploadImage__button--upload off">upload</button>

.off{background:red;    pointer-events: none;
    opacity: 0.3;}
.on{background:green;}

const file = document.querySelector('.popup-uploadImage__input');
const uploadBtn = document.querySelector('.popup-uploadImage__button--upload');
const deleteBtn = document.querySelector('.popup-uploadImage__button--delete');

file.oninput = () =>{
  if(file.value == ''){
    uploadBtn.classList.add('off');
    deleteBtn.classList.add('off');
    uploadBtn.classList.remove('on');
    deleteBtn.classList.remove('on');
  }else{
    uploadBtn.classList.add('on');
    deleteBtn.classList.add('on');
    uploadBtn.classList.remove('off');
    deleteBtn.classList.remove('off');
  }
}

deleteBtn.onclick = () =>{
  file.value = '';
}