On 16 March, the EU Parliament Research Service published a briefing which says that reflagging to a flag of convenience is a practice whereby a shipowner registers their ships in a country with relatively light controls or low standards, for instance in the area of environmental or employment law. While this is legal in principle, it is often combined with illegal practices, including the circumvention of sanctions. The IMO and the EU are trying to tackle abusive reflagging.
https://www.europarl.europa.eu/RegData/etudes/ATAG/2023/745686/EPRS_ATA(2023)745686_EN.pdf