Contacts sync with Disroot contacts

I would like to know how I can synchronize my contacts from Android’s native app “Contacts” with those from the Disroot cloud (in this sense, since on the contrary they do synchronize with DAVdroid).

You need to use DavDroid (recommended) or some other app that uses CardDav protocol to sync. Once the sync is done, you should see the contacts in your native/default app (you might need to setup in the app settings to display contacts from davdroid).