#1. First, enable Gallery Block Title

#2. Next, edit Image > Add some Title > Use this format with <em> tag
Title <em>Must go faster... go, go, go, go, go! God help us, we're in the hands of engineers. Hey, you know how I'm, like, always trying to save the planet? </em>

You will have a result like this

#3. Use this code to Page Header Code Injection (page where you use Gallery Block Grid)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
$(".image-slide-title").each(function(){
$(this).html($(this).text());
});
});
</script>
<script>
$(document).ready(function(){
$('.slide').each(function(){
var cr = $(this).find('.image-slide-title em');
var cr2 = $(this).find('.content-fill');
$(cr2).append(cr);
});
});
</script>
<style>
.image-slide-title em {
position: absolute;
top: 50%;
}
.slide .content-fill em {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
width: 100%;
height: 100%;
text-align: center;
display: flex;
align-items: center;
justify-content: center;
z-index: 99999;
}
.slide .content-fill {
position: relative;
}
.slide .content-fill:after {
content: "";
background-color: rgba(255,255,255,0.5);
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 999;
}
</style>

Result:
