To be honest, we struggle to find any difference between the portraits shot with the telephoto cams on both handsets. Varying from scene to scene, images from both flagships are sufficiently detailed while edge detection, aside from some small inconsistencies, is excellent. The bokeh on the 7 Pro, though, is more prominent.
And if the light isn't sufficient, you should maybe use the main camera. If you can, of course, because the 7 Pro doesn't give you the option to choose between its main camera and the telephoto - the portrait mode is locked on the telephoto. So as you've probably guessed, low-light portraits on the S10+ are considerably better using the main camera.
And a quick reminder - the 7 Pro uses the full 13MP resolution of the telephoto camera with around ~2.2x zoom instead of 8MP at 3x zoom like in the normal photo mode.
Both handsets perform equally well and as one would expect, the 7 Pro tends to capture more detail with its 16MP front shooter. Interestingly, enough, this is only true with portrait selfies. We believe it's because of HDR. As we already established, when HDR kicks in, 7 Pro's photos lose a bit of detail along the way so the effect might be the same with the front-facing camera as well. Overall, despite the lower resolution of the S10+'s front-facing shooter, things look just about the same when it comes to fine detail.
We woulds still prefer S10+'s rendition, however, as it produces more natural color skin, the dynamic range is somewhat better and colors are juicier. It also has a slight edge over the 7 Pro's selfie portrait because of the secondary camera for depth sensing. Not saying the 7 Pro's software for faux bokeh isn't impressive on its own.
Winner: The Galaxy S10+. Due to its flexibility with the normal and telephoto camera in portrait mode and better front-facing camera with autofocus, Samsung's flagship takes all the points in this category.