Using existing Gaia DR3 DL

I have a subset of the Gaia DR3 catalog (down to magnitude 15) already downloaded by Cartes du Ciel.

Can I just point Siril at that?

No.
We have built pour Gaïa catalogue specifically for Siril

I’m talking about the astrometric catalog, not the SPCC one. But it seems rather silly to me to have multiple copies of this huge catalog on the system, so I have to ask - why would you do that?

David

We already used shared catalogue with kstars. You can use it, but this is not gaia.
We built the astrometry catalogue to match our needs. But to be honest, we did not check what carte du ciel have done before.