You need to select a folder containing studiomdl.exe.

2 second web search: https://docs.blender.org/manual/en/latest/editors/nla/index.html

The tools export the full scene without regard to hidden objects or frame subsections, and this is by design.

You should be able to achieve this by setting up Non-Linear Animation (NLA) in your scene. This way you can select a subsection of the action either by cropping it, or by moving its track segment before scene frame 0.

Whoops, fixed this and released 3.2.2.

It looks a lot like the mesh & bones were imported with one up axis and the animation with another.

This is intentional. Units in SMD and DMX do not relate to any real-world measurement. Both the importer and exporter write whatever values they find in the scene at 1:1.

This is intentional in Blender 3.1.0 only. You can downgrade or wait for 3.1.1 to get the browse buttons back.

3.2.1 has now been properly released.

This is a bug in the preview version that I have since fixed. You can download the latest build from GitHub, and copy it into your Blender addons folder.

https://github.com/Artfunkel/BlenderSourceTools

This is due to a GUI error which was fixed in the preview that you said you downloaded in the other thread.