The Fourth Age of Blimnor, often called the Modern Age, is meant to resemble the Victorian Era of Earth, ranging between 1830-1910. This is because Blimnor is experiencing a similar period of industrial revolution, distancing itself from magic and other ancient conventions. To reinforce this, the fashion of this time period is similar to Victorian fashion. For some inspiration, here are a variety of costume pieces across the time period, genders, and social classes.
While the many nations and races of Blimnor may have distinct cultural clothing that may not be represented here, the growth of international trade results in a great deal of shared fashion, and a desire to fit in.
To stay compatible with the Dungeons and Dragons 5th Edition, exceptions to this will be plentiful. As an example: heavy steel armor pieces may not be appropriate for the period, but they are an important item for the game, so therefor they must exist. In other cases, things like cloaks, helmets, or medieval weapons, less explanation is needed, as some elements of Blimnor's history may simply linger out of tradition, or simply because they have changed shape to fit the aesthetic of the era.