I am making travel plans for May 2023 and will be spending some days in Trieste.
I would like to make a day trip from there to Rijeka, probably on a weekday (the most likely candidate is the 8th of May). I was unable to find any good information about ways to get to Rijeka in the morning and back to Trieste in the evening. For example, there seem to be no results when I search on the Flixbus website or some other bus operators' websites.
I would prefer to go by bus if one is available. I also have an EU driving license, so I could rent a car if there are no buses, but also do not know if there is a good place to rent a car that would be open at such early/late hours that I would be able to spend most of the day in Rijeka. (I also do not have any experience with renting cars, so information about how far ahead I would have to plan that is welcome too.)
Is there a good way to achieve what I want?