Fallback solo?

I can’t tell what you mean by “Fallback solo” from that alone.

Did you mean one of these?
- A musical term: “solo fallback” or a “fallback” part used when a lead vocal/instrument drops out
- A product feature in an app/game (a “fallback” solo mode)
- A specific song/track titled or described as “Fallback Solo”
- A software/AI behavior (a “fallback” mode or “solo” setting)

If you tell me the context (music, app/game name, or where you saw the phrase) and what you’re trying to do, I’ll give a precise answer.