Improve sound insulation of windows

What kind of windows are they anyway? Are they new or old? For old ones, a thorough adjustment and replacing the seals could help.

Hello Gerd,
Maybe an acoustic curtain will help you improve sound insulation. I once stayed at a hotel on a very noisy street, and there was an electric curtain installed. It really did its job. The curtain was very heavy, and to me, it felt like it had many different layers of fabric and at the bottom a kind of lead bead row. The beads kept the curtain taut. You could definitely notice much more what it "absorbed."

Since the OP does not mention how old the windows are, I would first check the adjustment and seals.

Then one could consider replacing the glass with a special one with acoustic insulation. In these, similar to laminated safety glass, a special film is usually inserted in the outer pane that reduces sound. No miracles should be expected, but 40-45dB are possible.

Probably the overall thickness of the glass composite (& the weight) changes and it must fit the window again.

Maybe say something about the existing window: material, age, frame manufacturer (if known). Current glass...