Cubase 11 Elements questions

I have done a few tracks lately using chord track, Halion Sonic, groove agent and arranger using all midi instruments.
I just recorded a track using chord pads, groove agent, arranger and I recorded a bass track with my bass guitar.
When I flatten the arranger track it all plays perfectly in the arranged sequence.
However when I export it to mix down in both wav or mp3 formats the playback on these tracks has only bass and drums. Is this because it is not all in a midi format?

No, that’s just how it works. There are a couple threads here about that.

Can you explain more please?