Can we use zinc plated screws for PCB grounding? Means the zinc coated screw head will be in contact with copper trace on PCB for grounding. But this can cause galvanic corrosion between zinc and copper. Can you all advise me on this topic? Can this cause galvanic corrosion?
If you can't tolerate corrosion then don't use zinc on copper. If you look on the table below zinc on copper is ADE which means plating is consumed and corrosion increased. Another thing to consider is if the copper is plated then it will be zinc on nickel but I don't have info on that.
You also have the option of printing solder paste over the OSP and reflow. I'm not recommending it, but I believe that's common with motherboards, for example. The main reason in that case would be for EMI mitigation, and perhaps nobody has checked motherboards for compliance after a few years.
Any connection that's not gas-tight has potential problems. If you really need a solid earth connection (for example, for safety) you may have to solder or stake a connector in.