ok…I know how to do it: Command A, Filter out the chords and move them manually from above the staves to between the staves. Like this I can hide the staves I don’t need and I still have my chords between the staves 
Correct. It strikes me as logical, though, that if you want chord symbols between the staves you need both staves present. How can Dorico obey the “between staves” rule, otherwise?
haha…you are right !