It makes no difference what you do for SEO reasons as long as you link the domains using the following:
<link rel="alternate" hreflang="es" href="https://www.domain.es/" />
You are telling Google that the above domain is for the Spanish language for the web page.
Google rates websites according to user location, so even if your website is number one in France and you link to the Spanish site, the Spanish one will not necessarily score as well in Spain, and the French one probably won't even appear.
I tested this with English sites. We have a co.uk & .com. In the UK, the co.uk site appeared top in search results, when I was in the US, the .com one positioned not as well, and this changed for each state.
I recommend highly adding Google analytics to the page so Google can monitor what users do as this will help your ranking. If you don't, how will Google know if someone went to the domain from an email or direct link?
Also make sure you set the HTML tag for each page according to the page language