How do I write 6/4 against 4/4 in Debussy Nuages ?

Debussy have wished a polyrhythmic or free feeling: the clouds are running in triplets in 6/4 against the englishhorns tuplets
I have tried alt-instert of 4/4 © in the English-horn. Wrong.
But how do I notate like Debussy ?

You need to use hidden tuplets for this.

O.K. But what about the 4/4 © symbol?

Create a time signature of C with a pickup bar 6 beats long. Then change the time signature back to 6/4 in the next bar and hide it.

Select the bar, press M, then type C,6 Alt-Enter in the popover so the time signature only applies to one staff.

Thanks to both of you. It works (- of course :smiley: )
Impressing what can be done in Dorico.

It worked fine. Thanks.