If you have issues after upgrading packages provided by your distribution, you have to let the person that maintains the package for that distribution know. Based on your information there is nothing actionable on our side. It is possible that they are modifying our source in ways we don't know, it is possible that they don't provide a recent enough version of mpg123... it could be many things.

Yes, as Saga Musix said, this really looks like a packaging problem. Nothing in libopenmpt changed regarding how we link libmpg123 between 0.7.11 and 0.7.12, as far as I am aware. If the problem still persists with the latest 0.7.13 package, please report the problem to the package maintainer of the RedHat 9 packages for ffmpeg or libopenmpt or mpg123. Once you did that, please also link to that issue here.

After a lot of searching and confusing RedHat vs Fedora branding, I think I found the package bug report at https://bugzilla.redhat.com/show_bug.cgi?id=2343160. I will close this issue. If there still turns out to be a bug on our side, it can be re-opened.