Which major European city was liberated for the first time by local military units on April 25, 1945, before the arrival of the Allies?

Milan was the first major European city to be liberated by its own people during World War II. Italian partisans launched a general insurrection against the remaining German and Fascist forces and took control of the city before Allied troops arrived. This was the collapse of Mussolini's regime. Today, 25 April is celebrated in Italy as Liberation Day.

https://en.wikipedia.org/wiki/Liberation_Day_(Italy)

It was Milan.

https://www.liberationroute.com/themed-routes/31/milan-the-capital-of-the-resistance?

The liberation of Genoa occurred following the insurrection which began on the night of April 23 and ended on the evening of April 26, 1945, with the arrival of the first contingents of Allied troops, who entered the city on the morning of April 27.
The only case in Europe, in Genoa, an entire German military contingent, under the command of General Gunther Meinhold, surrendered to the Resistance forces, without any allied war intervention.

https://www.museidigenova.it/en/act-surrender-german-troops-signed-genoa-april-25-1945