Multiple independent sources confirm the mayor of Koper (Slovenia) is Aleš Bržan1234.
The English Wikipedia entry lists the mayor as Aleš Bržan1, and the Slovene Wikipedia confirms he is the current mayor (župan) of the Urban Municipality of Koper, in office since 21 December 20185.
Official/institutional pages (Hidria, FEZ, FISU) and news outlets (RTV SLO) also identify Aleš Bržan as Mayor of Koper346.