Again, we do not and cannot support versions of Ardour built by 3rd parties). Please find an OpenSuSE support mechanism and ask them. Or get ardour from ardour.org/download - which we can offer support for.
No, it wouldn’t because this is likely a build error. I am assuming you are using Ardour 6.0.
If it is Ardour 5.x, then yes, documentation on how to do mp3 export with that version would have been nice to have in the manual. However, 6.0 now has mp3 support builtin and so such documentation would be out of date. We have very very few contributors to the manual (much, much less than developers).
Just a question: mp3 export option is missing in my install or am I looking in a wrong place?
If is missing I’ll send a question or a bug report to Archlinux package maintainer.