For all citizens of the EU countries, it is now possible to enter Croatia without a subsequent mandatory quarantine. According to the Croatian Ministry of the Interior, entry can take place if there is an important reason. This also includes booking a hotel, an apartment or, for example, a charter boat. Find it on the German-language page https://mup.gov.hr/uzg-covid/deutsch/286213 answers to frequently asked questions about entry. It also indicates which documents are required for entry.
With regard to transit through countries such as Slovenia and Austria, the green light has now also been given. Thus, a vacation in Croatia, e.g. in our apartments, nothing more in the way. The respective embassies also provide further information, e.g. for German citizens: https://zagreb.diplo.de/hr- com / coronavirus-information-for-travelers-to-croatia / 2318008 .