It may different by local culture, but I have tech colleagues who take care about how they look and are pretty stylish. Not really suits, but officially looking shirt. I did not noticed any discrimination against them.

There is also big difference between formal rules you can be fired for not following and informal ones - informal are still limiting but people cross them once in a while and you often finds it is actually ok in the long term.

People like to generalize tech as if everything would be stereotypical frat like start up, but it is not the case.