A halftone is not supposed to be transparent, so do not add any adjustment layer to it.
Look at the difference between these two images. The one on the left has no transparency on the layer itself. The one on the right has gradient transparency.
In order to do the effect, I do not have Ps right now, but in general:
- Make a new rectangular grayscale gradient from pure black to pure white. You do not want those white dots you have on your image.
- Transform it to a 1-bit image with Halftone. Play with it.
- Put it over your image with "If lighter".
P.S. In order to have a smooth dot, the source image needs to be at high resolution. If you can make it 600-1200 PPI.
Using 1 bit image can make the edges a bit rough on small resolutions.
In that case, you could make the gradient at a high scale, make it halftone, convert it to grayscale again, and resample it. But you can not use it with "If Lighter" blending mode, but you can now use it as a mask for a flat white color layer.