Please, either paste the output here (it is not that long, and it makes it possible to comment and answer in context) or for the very long output upload to https://susepaste.org/ to avoid commercial sites with advertisements, JavaScripts etc.
Anyway, different components of mpg123 are installed from different repositories (projects). Any reason you are using development project at all? At least, make sure everything is installed from one location.
Removed mpg123, mpg123-openal, mpg123-pulse and libmpg123-0-32bit, and installed mpg123 as
# zypper in -r openSUSE:Leap:15.5 mpg123
Now it does show mpg123 --help, but gives another error when I try to play something:
> mpg123 171184669_151973837.mp3
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layers 1, 2 and 3
version 1.26.4; written and copyright by Michael Hipp and others
free software (LGPL) without any warranty but with best wishes
[src/libout123/module.c:open_module_here():133] error: Failed to open module openal.
[src/libout123/libout123.c:out123_open():440] error: Found no driver out of [alsa,oss,jack,portaudio,pulse,sdl,openal] working with device <default>.
main: [src/mpg123.c:324] error: out123 error 3: failure loading driver module
I have followed this and produced the file /etc/asound.conf with the same content as there, but this doesn’t help. I have installed also mpg123-pulse; this hasn’t help as well.