Is it correct that for Magento2 CE there is now only the possibility of a master database server, EE it is understood that there is the split database functionality however 1.9x allowed for a master and also read slave.
According to the docs it looks like it, yes. Buit-in split database functionality (CQRS) is only supported in Magento 2 EE.
"In Magento Community Edition (CE), only one master database is used."
Although it will not give you out of the box read/write segregation, you could work around some of the scalability issues with a single DB by using Galera cluster with master-master replication.
That is correct, Magento 1.x allowed master/slave databases whereas Magento2 is single database with only the enterprise edition allowing replicated databases. Always nice to go backwards, so the architects told us to do the same and we are reverting back to 1.9x. To coerce Magento2 you can use a single endpoint as suggested Galera, but that is a maintenance headache.