Although there have been seasons when Optima has picked up / set down passengers in Ljubljana, we don't think they are currently doing that. The 2021 season has just two more weeks to run and trains are running with no scheduled stop from Villach to Edirne. Also perhaps worth mentioning that this Optima train hasn’t had sleeping cars recently. Passengers are all accommodated in couchettes. There is also a restaurant car. 

S&N / hidden europe / Berlin 

The OptimaExpress is sadly not included in Interrail/Eurail

The trains Belgrade - Sofia and Sofia - Istanbul are currently suspended

You could go Lubljana - Budapest - Bucharest - Sofia - Swilengrad by train and then just the last few kilometers by Taxi or Bus as currently no international trains to Turkey :/