Many are still there.

A grand total of 120 000 mines are present in the Baltic Sea, some 20-30 000 of them in the Bay of Finland alone. Roughly half them still are still active. There are about 40 000 mines from ww1, ww2 and the cold war in the Swedish part of the Baltic Sea alone. Many have rusted and sunk by their anchor others have moved with undersea currents and drifting ice. Yet others have torn free from their anchors in storms or in ice drift during the winter. There's usually mines drifting ashore in Sweden every Spring and Summer and some being caught in fishing trawls - some are of ww2 vintage, but most are more recent as the older mines usually sink when their outer hull rusts through.

Mines were built to be cheap weapons to deploy en masse and in the Baltic Sea often to be swept and taken back in during Winter and laid out back again in Spring, so many of them have rusted through completely.

Here's an image from the Swedish armed forces detailing where there's still mines in the Baltic and North Sea. As you can see, there's quite a few mines still around.

During the construction of the NordStream gas pipeline and the projecting for the NordSteam 2 gas pipeline on the bottom of the Baltic Sea, extensive mapping of the bottom of the sea and clearing of mines have been conducted to ensure the safety both of the workers laying the pipeline and the pipeline itself.

In June 1945, immediately after ww2, the Western Allies and Denmark used roughly 27 000 captured Kriegsmarine sailors in the German Mine Sweeping Administration (GSMA) organisation on 300 smaller vessels to sweep the sealanes in the Baltic and North Sea of mines. The organisation was dissolved in January 1948.

In general, the sea lanes have been swept, but not counting the NordStream project, most other mines are still there.