Romanianflyer

Possible in theory, IF you can find a rental agency willing to do this.

As written before, not many agencies in this part of Europe are keen on having their cars being taken over the border. Especially not the big international chains! I would recommend to start checking local rental companies first. I'm quite sure that after contacting a few of them you will already get an idea how difficult this entire idea is.

Simply put, you need permission from the rental company (a written document signed by them!) stating that you are first of all allowed to take a car across the border and second of all that it's fully insured in third countries. Without this, you will simply not make it with your rental car from North Macedonia into any of the neighbouring countries (or with a Montenegrin rental car to Serbia, with an Albanian car to Montenegro or whatever other border). This document will be asked for by the border guards at all international borders.

Basically, with that letter comes full cross-border insurance as well. If something goes wrong, the rental company needs to pick up the car 100s of miles from their home country or somehow arrange repairs. This is why often such a permission/document is not given in the first place, and if you find a car company willing to do so, you can expect a hefty daily surcharge for each day you are taking the car out of the country where you are renting it.

Now some rentals might be very well possible. A Croatian car rental company might allow you entry into Bosnia, or a Montenegrin one into Serbia and Croatia. These are countries with relatively close links to each other. But I wouldn't count on any other country allowing their cars into Albania, for example. Again, politics! And some countries not having the best reputation when it comes to road quality and tolerance towards certain foreign number plates, whether this is fair or unfair is another discussion, but it's just the way how it is. You can thus also completely forget about finding one-way rentals in this region - I'd be surprised if you can find one at all, let alone one which is reasonably priced.

To give you an idea how complicated it is with rental cars: once me and some friends decided it was easier to BUY a 2nd hand car in Bulgaria as it was cheaper and easier with paperwork than doing a 2-week rental to tour the Balkans

For a multi-country trip in this region, the fact is that you will be reliant on public transport. It's just the local way of life: you either have your own car, or you take a bus/minibus. It's not luxurious, it's not fast, but there are good links between all the main cities. Train service in this part of Europe is highly limited, with the only services which are currently worth taking being Bar/Podgorica (Montenegro) to Belgrade (one of Europe's most scenic rides, highly recommended!) and Split to Zagreb. Dubrovnik has no rail connections, and even the closest station of Ploce which was mentioned above currently has no service (the Ploce-Mostar-Sarajevo line nowadays only sees a rail service on the Bosnian stretch between Mostar and Sarajevo, which is scenic too). Due to corona/track works there aren't even rail links between Croatia and Serbia at the moment...