Short answer : You're the GM. It's your world, you determine what would be appropriate...and also, based on that character's background and skillset, if they would know what is appropriate.
Long answer : This is highly situational, regional, and cultural. What is appropriate in a board room in New York is very different than in Miami, or Brasilia, or Bangkok, or London, or Moscow. What is appropriate in the boardroom of Seader-Krupp is different than Horizon, or Spinrad, or Ares, or Mitsuhama, or Aztechnology.
What you'd wear in federal court would get you bounced from a high society black tie event, and killed in the Barrens. What you wear to an AAAT meeting wouldn't fly at HOAA.
Neon/Steam/Cyberpunk attire may in fact be mainstream in your setting, and may be appropriate in many places -- but I'd look to things like Availability and bespoke suits that give social stat bonuses to determine what is appropriate in higher society and corporate board rooms.
Of course, Runners are generally SINless untouchables, anyway. If they're being hired for jobs that require "acceptable" attire, Mr. Johnson should be providing it, or hiring Runners of high enough standing to know that Hawaiian Netsurfer wear is not what one wears to a gala at the Tir Ambassador's residence.
-Jn-
Ifriti Sophist