Travel from Prague to Croatia (either Split or Dubrovnik)

Probably train, maybe flight.
If you are not familiar with train travel, here's a good resource:
https://www.seat61.com

More information will get you a better answer.

Unless either a 20-hour train or a 15-hour bus appeals to you, I’d recommend flying PRG to SPU ( Split) in 90 minutes for about $150. www.Skyscanner.com

Hi,
We made a similar trip some years ago by train and made the move from one location to the other a chance to visit cities between the two points. Brataslava, Budapest, and Zagreb. But we had plenty of time. And we enjoy the ease of train travel. Praha, Vienna, Zagreb would also be nice and break up the train ride.

Maybe the real issue is, are you going to both Split and Dubrovnik or only one? Split is partially built within the outline of Diocletian's palace and seemed more real. Real locals. Real businesses. In the city center. Dubrovnik is really about what is inside the walls of the old city and that seemed small and pretty tourist filled. Restaurants for tourists, Trinkets for sale.

If you can do both, great. and don't skip a day trip to Ston or the islands.

wayne iNWI

In the summer there are direct night trains from Prague to Split.

https://www.seat61.com/international-trains/trains-from-Prague.htm#Prague-Dubrovnik