It may be too early to see and book all specific options. Airlines may add routes or schedules yet and buses usually don't publish schedules more than a half a year in advance (often even less).
- Fly direct to Trieste (1:20) + bus to Ljubljana (1:44)
- Volotea flies direct, but only shows schedules through July 2nd 2020. They have a 1:20 flight on Monday June 29th for €47. It may be worth contacting them to see if they are terminating the route or if schedules have just not been released yet.
- Several bus lines run between Trieste and Ljubljana, but looks like only one departs the airport (though the July schedule isn't out yet). It's tight connection to that flight: risky but very quick.
- Fly direct to Treviso (1:20) + bus to Ljubljana (2:30)
- Ryanair has two direct flights on July 6th. 7am and 7pm for €30-40. They call the airport "Venice Treviso"
- DRD Turizem, GoOpti, Nomago and TripstAir all run from TSF Airport to Ljubljana, again the July schedule isn't out yet but you should be able to find a decent connection with frequent departures.
- Fly direct to Venice Marco Polo (1:20) + bus to Ljubljana (2:49)
- Fly direct to Venice Marco Polo (1:20) + bus to Ljubljana (2:49)
- easyJet has two direct flights on July 6th. 7am and 7pm for €25.
- DRD Turizem, GoOpti, Nomago, TripstAir and FlixBus all run from VCE Airport to Ljubljana, again the July schedule isn't out yet but you should be able to find a decent connection with frequent departures.
Full disclosure: I work for Busbud, the site showing various bus lines.