Trieste-- Ubers and Taxis

I took a taxi doing exactly this in 2019. No issues.

In case you are doing the same, I did this as part of a rental car shuffle. I dropped off, taxied and picked up in Slovenia. It went fine.

Taxis and NCC - point to point drivers - are your private transfer options in Italy. Uber is essentially only a limo company in Italy and they may be able to help you with this transfer but it is not the same as Uber in other companies.

There is also a twice a day bus but if the taxi option is available it's certainly easier if not cheaper.

Have a great trip,
=Tod

We used daytrip.com for 3 people going from Venice to Rovinj, Croatia. It was more expensive than the bus but also more convenient and comfortable.

Both countries are in Schengen area, you'll have no problems with border crossings and administrative things.
Note that companies like daytrip, uber, tripadvisor etc are intermediaries that use local companies, add their fee and sell. I would suggest booking local one, you'll get absolutely same service, for less money, sometimes 30-40% lower price.

A taxi will cost you at least 50€

There is also the Arriva Slovenia bus:
https://arriva.si/

Flixbus also operates a few runs a day