I think that "business suits" are fading after a good long run: not too long ago men wore suits to any office job, and before that (if old movies and TV is accurate) just about always, if not a different work uniform.
Now "business casual" is taken hold.
Some ideas for you, which may not be right but are plausible for your story:
Men's clothing will become more varied.
"Nice" attire will be much less formal looking to our eyes, but will be (e.g.) not torn or distressed, not have logos or slogans, and be more complex than strictly comfortable clothes. Being "formal" will seem like arbitrary decisions on which colors, styles, or other attributes are more or less formal. Probably not bright colors for "formality".
Clothing will be "smart", with wearable electronics. Clothes can be reactive and adaptive, such as changing color or warmth.
There have already been some products that uses nanotechnology to make cloth seem like plastic sheeting when liquid is spilled on them. I expect that will be perfected, or so cheap that you don't care if it can't survive being washed. Maybe cleaning will involve re-initializing the repellent technology. And with all the difficulty in washing something that repels water and oil, you also have it not needing to be washed because it doesn't get dirty. Maybe have an "air" treatment that blows out adsorbed odors and trapped molecules, without getting it wet.
New materials like carbon fiber. Not sure what good carbon fiber is for normal clothes, but aerogel fabric is already available for insulating. Just like arcticware was revolutionized already with modern 20th century materials, that can have another round: the warmest coat anyone can ever need would be as thick as a moderate winter coat today, and normal winterware looks like today's light jackets.
T-shirts will light up and have active displays, not just static printed art.
How about new forms of fasteners? We've seen the invention of the zipper, more recently shoelaces give way to velcro, and velcro cuffs for gloves and such. Maybe stretchy elastic that doesn't bunch up but looks neat across a large range of length stretch. But could some new form of fastener catch on? What about magnets? Something as strong as a rare-earth magnet but flat embedded into the cloth could replace some buttons and snaps, especially in "formal" clothes where you like the clean unbroken appearance.
For adding to the story, think about specific fashion trends. Hats have come and gone, and could come again. Perhaps neckties will be replaced with cravats that are comfortably loose, with style in different ways of tying it.
Here's a thought on form-follows-function. I notice how a vest (wastecoat) has little pockets meant to hold a watch. That was a practical design originally, now frozen as style. Today just about everyone needs to wear displayed ID, often using a lanyard. Could that evolve into a functional element of business attire? A clear pocket to hold the ID card, perhaps?