Regarding your world, I would first like to address that from a historical standpoint, there’s a significant gap (~300 years) between the medieval age and the Victorian era. These time periods are distinguishable by their technological developments, including architecture. Superficially, Victorian architecture drew a lot from Gothic architecture, which was developed in the Middle Ages. However, a lot of the styles present in Victorian architecture used techniques far too advanced for the medieval era.
On the outside, the typical Victorian building and Gothic building look similar. On the inside, however, differences in building materials and advancements in design are clear. Victorian buildings are generally more open because advancements in design allowed them to build “out” as well as up. Comparatively, Gothic buildings are more “narrow,” with more emphasis on structural integrity (such as ribbed or vaulted ceilings). This is more obvious in grand structures, such as cathedrals, than it is in smaller buildings, such as common city dwellings. In addition, medieval architecture relied on stone (such as limestone and sandstone), which is heavy and often weak (particularly against the elements). Victorian buildings were known to incorporate stronger materials, such as steel and concrete, in addition to the classical materials, such as stone and wood.
On the other hand, the use of magic in your world means that your architects may have a means to design and construct buildings that surpass even those of the Victorian Era, in terms of size and stability. Your city could have magically enhanced Victorian-style buildings made with medieval-era technology (this might be an interesting thing to explore— what happens when the magic fails?). Ultimately, this is up to you, depending on the potency of magic in your world.
Lastly, you mentioned longer twilights and the supernatural, so I wanted to tie that in as well. These themes might not make a huge impact structurally, but they could influence how the buildings are presented and decorated. Depending on the mood of your capital, the buildings might be painted in bright colors to stand out in the dusk, or dark colors to blend in and avoid drawing the attention of the supernatural. They could also influence the layout of your city. Perhaps the buildings are spaced far apart so that it’s harder to hide during the dark hours. Maybe they’re wedged as close together as possible to make it harder to run. It would really depend on how the supernatural occurrences are perceived by the architects of the city.
Architecture is one of the coolest aspects of history, so props to you for taking that into account right out of the gate. I wish you luck as you build your setting!