Osijek is a city in Croatia.
Currently most international traffic is bypassing Osijek. There is a hitchable spot on the bypass at 45.56972, 18.63262, but it doesn't seem very easy to get there and hitchhike. Instead, you can get to Beli Manastir by train or by hitchhiking from Biljska cesta street. Much long distance traffic is passing through Beli Manastir and the border crossing afterwards as it is known for lesser delays than the crossings between Serbia and Hungary. On Sundays, many exYu people are returning from their family visits to Austria and Germany. Duffajfka found a car going all the way to Munich from the border in September 2021.
SOUTH-WEST to Bosnia(Banja Luka)
Going from Osijek to Bosnia toward Banja Luka. You could try to go on high way(E73) that leads back from Osijek to Zagreb just before pay tolls, try to catch a ride to Nova Gradiska and than you are not so far away from Bosnia(driver will probably leave you just before border). On this high way from Osijek to Đakovo it is not so good traffic and cars are going very rarely so maybe it is better to take normal road to Bosnia but you could try your luck(later when pass Đakovo and you drive at A3 high way there is much better traffic). People probably do not use often this high way because you must pay fee for driving there and normal road is free.