A “cheap” solution is to make the coda start on a new system.
You can hide the system barline including the brace in the properties, and you can insert an (explicit) invisible clef to replace the treble clef, a problem is the bass clef.
And if playback is not important of course you can fake the Coda expression with System Text.
Thank you Vadian.
I’m very surprised that Dorico doesn’t offer more flexibility here, and has decided that a coda must always be preceded by a space – which is standard practice in rock and pop, but certainly not in classical music. I’m extremely disappointed by this.
For the gap, this is OK, (Whether it’s the option I’m showing in the Engrave Options menu, or the settings you’ve specified), the problem is that the clefs remain, and at mid-measure, it’s impossible.
I finally chosen the Coda sign in Text (Shift+X) as @Vadian suggested ; fortunately, the playback will not be used in my score.