Thanks for your question, which has come up in different ways several times before.
Galleries generated by [mla_gallery] include class attributes that help you apply CSS styles to each gallery element. Formatting can be customized by defining CSS styles in your theme’s stylesheet(s) or in the post/page where the gallery appears.
However, I regret that I have never found a solution for adjusting the height of an image dynamically to fit the browser window in which it appears. There are many techniques for adjusting width but I have not found corresponding techniques for adjusting height.
You could, of course, use some JavaScript code to achieve your goal.
I regret the news is not better, but I am marking this topic resolved simply because I have answered the question to the best of my ability. If you find a solution I encourage you to post it here so I and other MLA users can benefit from your discovery. Thanks for your understanding and for your interest in the plugin.
I need this in all galleries on WP and I set max-height: 80vh to style.css of my theme.
.gallery img {
border: 10px solid #f1f1f1;
max-height: 80vh;
width:auto;
}