Salzburg to Split in 10 days

Those all look like pleasant stops, but you have not told us anything about your goals or interests.
What kind of drop off fee did you find you’ll be charged?

Have you checked what the drop charge is going to be?

I have been to Rijeka, near Kraljevica, Trojir and Split. Enjoyed them quite a bit. Split deserves more than one day for sure.
Trojir was great for one day it was special.

mh1776,
Just a warning, the driop off fee in a different country could be 500-1000 euros.

mh1776,
In speaking with friends here in the US, there seems to be the idea that driving a car from one country to another and dropping it there is like going from one state here to another. They are always surprised when they realize that it is considerably more complicated. Distances also seem to be very much underestimated as well, and the fact that there may not be interstates everywhere isn't understood. Do check out travel times between these locations. And if you do decide to, and are allowed to, drive on this whole trip, add some time to the quotes from websites. They rarely factor in time for gas/food/comfort stops, so you need to do so.

every country has their own laws, their on bureaucracy, their own
traffic rules, their own culture, their own language,

Texas has its own laws, its own bureaucracy, its own traffic rules, its own culture, its own language (sort of, like Bavaria and Austria).

rei,beaten,
Yes, that is my point exactly. I am not assuming they are the same. I am saying that many US travelers to Europe make that assumption. I DO know the difference.

rei.beate,
Sorry about the name typo. Autoc correct.