I'm created a vector map in photoshop and I used rectangular shapes and merged them. But when I tried to export as a SVG, the intersections between them became transparent 😕 I don't know what to do to solve this.
Your original shapes are transparent to begin with - is this intentional?
The quick fix is to export, duplicate the layer a few times and merge. That will obviously rasterize all the shapes.
Of course, transparency shouldn't add up this way. It looks like a glitch in layer compositing. What version are you running? There's been a problem with the new GPU compositing, so it's been removed entirely in the latest 23.4.1.