Deneyebilir misiniz?
<div class="project-slider owl-carousel owl-theme">
    <?php
    $psor = $db->prepare("SELECT * FROM projeler WHERE anasayfa=? AND dil=? ORDER BY id ASC");
    $psor->execute(array("1", $_SESSION['dil']));
    $pisl = $psor->fetchALL(PDO::FETCH_ASSOC);
    
    $array_new1 = array();
    
    foreach ($pisl as $pson){
        array_push($array_new1,$pson);
    }
    array_multisort(array_column($array_new1, 'id'), SORT_ASC, $array_new1);
    ?>
    
    <?php
    foreach ($array_new1 as $pson) {
    ?>
    <div class="single-project">
        <?php
        $rsor = $db->prepare("SELECT * FROM projeresim WHERE rid=? ORDER BY id ASC");
        $rsor->execute(array($pson['id']));
        $risl = $rsor->fetchALL(PDO::FETCH_ASSOC);
        $ilkResim = true;
        $array_new2 = array();
        foreach ($risl as $rson){
            array_push($array_new2,$rson);
        }
            array_multisort(array_column($array_new2, 'id'), SORT_ASC, $array_new2);
        
        foreach ($array_new2 as $rson){
            $resimURL = "/".tema."/uploads/projeler/diger/".$rson['resim'];
            if ($ilkResim){
        ?>
        <a title="" class="popup-btn" href="<?=$resimURL;?>"><img src="<?=$resimURL;?>" alt="" class="project-img"></a>
        <?
        $ilkResim = false;
            } else {
        ?>
        <a class="popup-btn" href="<?=$resimURL;?>" style="display: none;"></a>
        <?
        }
        }
        
        
        
        ?>
        <div class="fancybox"><i class="bx bx-expand" aria-hidden="true"></i></div>
    </div>
    
    <?php
    }
    ?>
</div>