I was literally just researching how to do that yesterday (told you I was serious). It turns out that those threaded holes in sheet metal with the little dimples so there’s more thread than the sheet metal thickness are made with “roll taps” or “forming taps,” not “cutting taps” (which is what your tap and die set probably is). Instead of creating chips, they push the metal out of the way to form the threads.

By the way, similarly thickened but unthreaded holes are made with something called a “friction drill.” It doesn’t have any flutes, so it just heats up the metal until it gets soft and gets pushed out of the way. Kinda neat.

Anyway, I just ordered a 6-32 forming tap off AliExpress; I’m gonna see if I can add some more motherboard standoff holes to one of my computer cases because it’s big enough for an EATX board but isn’t drilled for it.