Take a look at the (included with Audacity) “Fade Ends” macro to see how to do that. Basically, you will need to select 0.5 seconds relative to the end of the track, and then apply a Fade Out.
Read my previous reply again, and look at the “Fade Ends” macro to see how that macro applies fades to the ends. There’s not much more I can tell you - the information is all there.
So I need to select the last 0.5 seconds of each file? But I need to do it as a batch for multiple files. Is there a way to select the last 0.5 seconds for each open file?