And it does not show docx files. Seems to only work for images and pdf files.
Thanks for your question. From the examples you have already found you can see that the post_mime_type parameter is the key to getting the results you want. The simplest example I can think of is:
[mla_gallery post_mime_type=all attachment_category=some-category]
If you want a more list-like format and a direct link to the document file you can try something like:
[mla_gallery columns=1 link=file size=icon post_mime_type=all attachment_category=some-category]
In this example, size=icon will give you thumbnail images for the non-image items. If you want to replace the default captions with your document titles, try:
[mla_gallery mla_caption="{+title+}" columns=1 link=file size=icon post_mime_type=all attachment_category=some-category]
You may have already found this earlier topic, which has links to several topics dealing with list formatting applications:
Simple list
If the above suggestions are not working for you, post the source text of your shortcode(s) and any additional information you think useful and I will look more closely at your application.
I am marking this topic resolved, but please update it if you have problems or further questions about using [mla_gallery] to display non-image Media Library items. Thanks for your interest in the plugin.