dizelvis,
возможно вы хотели так ...
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@fancyapps/fancybox@3.5.6/dist/jquery.fancybox.min.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fancyapps/fancybox@3.5.6/dist/jquery.fancybox.min.css">
<script>
$(function() {
$.fancybox.defaults.beforeShow = function(instance, slide){
var index = slide.index;
var style = $('.imglist img').eq(index).attr('style')
slide.$slide.attr('style', style);
};
});
</script>
</head>
<body>
<h2>fancybox v3.5 - Initialize with data attributes</h2>
<p>
Groups are created by adding the same <code>data-fancybox</code> attribute value
</p>
<hr class="my-5" />
<p class="imglist" style="max-width: 1000px;">
<a href="https://source.unsplash.com/juHayWuaaoQ/1500x1000" data-fancybox="images" data-caption="Backpackers following a dirt trail">
<img src="https://source.unsplash.com/juHayWuaaoQ/240x160" style="transform: scaleX(1) rotate(90deg)" />
</a>
<a href="https://source.unsplash.com/eWFdaPRFjwE/1500x1000" data-fancybox="images" data-caption="Mallorca, Llubí, Spain">
<img src="https://source.unsplash.com/eWFdaPRFjwE/240x160" />
</a>
<a href="https://source.unsplash.com/c1JxO-uAZd0/1500x1000" data-fancybox="images" data-caption="Danish summer">
<img src="https://source.unsplash.com/c1JxO-uAZd0/240x160" style="transform: scaleX(1) rotate(90deg)" />
</a>
<a href="https://source.unsplash.com/eXHeq48Z-Q4/1500x1000" data-fancybox="images" data-caption="Sunrise above a sandy beach">
<img src="https://source.unsplash.com/eXHeq48Z-Q4/240x160" />
</a>
<a href="https://source.unsplash.com/RFgO9B_OR4g/1500x1000" data-fancybox="images" data-caption="Woman on a slope by the shore">
<img src="https://source.unsplash.com/RFgO9B_OR4g/240x160" style="transform: scaleX(1) rotate(90deg)"/>
</a>
<a href="https://source.unsplash.com/7bwQXzbF6KE/1500x1000" data-fancybox="images" data-caption="Mountain hiking sunset">
<img src="https://source.unsplash.com/7bwQXzbF6KE/240x160" />
</a>
<a href="https://source.unsplash.com/NhU0nUR7920/1500x1000" data-fancybox="images" data-caption="Sunset Picnic">
<img src="https://source.unsplash.com/NhU0nUR7920/240x160" style="transform: scaleX(1) rotate(90deg)"/>
</a>
<a href="https://source.unsplash.com/B2LYYV9-y0s/1500x1000" data-fancybox="images" data-caption="On them Indiana Nights">
<img src="https://source.unsplash.com/B2LYYV9-y0s/240x160" />
</a>
</p></body>
</html>