<input type="checkbox" id="popup1" class="popupAc">
<input type="checkbox" id="popup2" class="popupAc">


<div id="mycheckboxdiv_popup1" style="display:none">
<div id="popup1" class="overlay">
<div class="popup">
<h2>Uyarı !</h2>
<a id="kapat"><i class="fas fa-times"></i></a>
<div class="content">
İçerik Alanı 11111111111
</div>
</div>
</div>
</div>

<div id="mycheckboxdiv_popup2" style="display:none">
<div id="popup1" class="overlay">
<div class="popup">
<h2>Uyarı !</h2>
<a id="kapat"><i class="fas fa-times"></i></a>
<div class="content">
İçerik Alanı 22222222222
</div>
</div>
</div>
</div>

$(document).ready(function() {
$('.popupAc').change(function() {
let cid=this.id;
$('#mycheckboxdiv_'+cid).toggle();

});
});