Another question about MongoDB : what is the best way to do if I have to sync data every 4h ? I have the feeling that the standard way import and overwrite all the data again and again, I'd hope there is something like CDC for MySQL : wdyt?

I'm assuming you've read through the mysql docs? https://docs.airbyte.com/integrations/sources/mysql/

yes, does it exist the same method for a MongoDB database ?

MySQL doesn’t support dedup yet