From time to time I got the need to trim intros/outros or silence from downloaded audio files.
I’m currently using Super Sound, but I find it a little silly that one of the last closed source, filled with ads app I still have installed is for such a small functionality.
On desktop I use ffmpeg for pretty much anything, so if there is some wrapper for it over android it would be ideal.
If you are comfortable with ffmpeg you can give termux a try. I used ffmpeg through it in the past to occasionally snip out parts from mp4’s and that worked like a charm.