For Hungary you have this (1495):
I know its only a part of the region but may be useful.
Furthermore, let's go by areas:
Wallachia and Moldavia were almost entirely Romanian
Dobruja was Bulgarian-Romanian-Gagauz mixed
The area of current Albania was entirely Albanian besides north Epirus which was mixed greek-albanian.
The main issue is placing the extent of Bulgarians and Greeks, because the population movements were continuous: as far as we're concerned, Bulgarians were the majority of the population within modern-day Bulgaria, North Macedonia and the southeast of Serbia. Greeks were the majority in the same areas as in the 19th century maps, adding southern Bulgaria, southern North Macedonia and the Black Sea coasts of Bulgaria, containing them a minority of Bulgarians (approximately, some areas already may have Bulgarian majority).
If you remove the Turks from the 19th century maps, the ethnic makeup isn't much different than it was then.