There is a lot of misinformation and bad advice on the internet. It's travel specific, and since Travel + Leisure can help itself, I guess I can help myself as well.
No, of course they don't. Why would anyone think that? Travel + Leisure wrote a story about what to wear to increase your chances of a first class upgrade.
This seems to be a thinly veiled attempt at getting some affiliate revenue by posting links to clothing that will get you an upgrade. I think posting links to credit cards that can score you first class seats is a better business model.
The Travel + Leisure piece is based on a story wherecabin crew share the outfit that will get you bumped up to first class.
“For an upgrade, it’s all about looking the part. Smart but understated. You should look like you travel often. But don’t be dripping in designer clothing. It helps; someone who is potentially due to get an upgrade can be knocked back if they aren’t dressed suitably.”
Dressing up won't increase your odds of getting a first class upgrade. Period.
Every airline has protocols for awarding upgrades. There are a variety of ways to score a first class seat, aside from paying cash for it.
There are some situations where flights might be oversold in economy, and there are empty seats in first class, and no one on the upgrade list. An operational upgrade is when airlines need to raise people up to first class.
There is a very specific procedure for doing that in these situations. The policy varies by airline, but typically operational upgrades are prioritized by elite status and/or the fare class you're booked in.
If you are traveling alone and the airline needs to seat a family together, you may be bumped up to an exit row or economy seat.
The gate agent doesn't send RuPaul into the gate area to see who is serving the best looks.
I think this is where the confusion might come from, because generally speaking there isn't. Airline employees can fly for free or at a heavily discounted rate on a space available basis. Employees can fly in first class, but only after all other upgrades have been completed.
If you want to fly in a premium cabin on an airline, you should be aware of the dress codes for employees. The only time there is going to be a dress code is that.
I think there may have been more truth to this back in the day. Gate agents had more discretion to upgrade people, even if they were friends, because they were trying to hit on them.
What has changed?
It wasn't unusual for a gate agent to violate policy and upgrade an employee friend ahead of a passenger. Nowadays upgrade lists are usually published so the person on the upgrade list knows what's going on.
Dressing up won't get you a first class upgrade, so dress for comfort when you fly. There are many ways to score a first class seat nowadays, from having elite status to redeeming miles.
Dressing up is the key to scoring a first class upgrade according to the urban legend.