On 31 March 2024, Romania and Bulgaria joined the Schengen area. This means, controls at internal air and sea borders between Bulgaria and Romania and countries of the Schengen area will be lifted. For the time being and until a further decision, checks at internal land borders remain in place.
The border-free Schengen Area guarantees free movement to more than 425 million EU citizens, along with non-EU nationals living in the EU or visiting the EU as tourists, exchange students or for business purposes (anyone legally present in the EU). Free movement of persons enables every EU citizen to travel, work and live in an EU country without special formalities. Schengen underpins this freedom by enabling citizens to move around the Schengen Area without being subject to border checks.
More on Schengen: https://home-affairs.ec.europa.eu/policies/schengen-borders-and-visa/schengen-area_en