I've gotten a job offer from every technical interview I ever took in a suit, so it Worked For Me. And none of the jobs that I took I ever wore a suit to again (except for conferences or trade shows, and occasionally when I was going out after work to somewhere posh, which did provoke fun "Omg are you interviewing" questions!) Which I actually have found a bit of a shame because I do quite like a chance to wear a suit, though I'm also grateful not to have to iron infinite shirts.

Admittedly I thankfully wasn't in the SV bubble where people are wound this tightly about it!

An interview is not a regular work day. If only things relevant to the job were required in an interview, no one would be talking about whiteboard exercises.

It's a red flag? Come on, if I wear a suit it's because I want too and has no impact on my skills as a software engineer.

Being hyper judgemental about the clothes people wear isn't productive

If it's so important, the interview invite should mention that casual wear is expected. Like it or not, most people take interviews seriously, and have been taught that you show you take the interview seriously by wearing a suit.

Which is funny, because weren't we in tech the people who aspired to “think different”? But then it didn't become think-different for the individual but for the tech in-group against the "square", boring, formality-driven out-group. And since the world is becoming increasingly informal and any group worth its salt needs to differentiate itself, tech people might be the first to return to wearing suits and ties (or dresses) to work. I'd love that.

With reference to the GP about awkward people, if an adult hiring manager is intimidated by an professional applicant wearing a suit to an interview in good faith (after all, it's widely seen as mark of taking the interview seriously), I think it is perhaps not the applicant who need to learn the social skills.

If an interviewer can't tell the difference between a flex and show of good intent, they probably should go back to jobs where they don't need to make judgements of character.