There's double trigger RSUs and so on that allow you to have reasonable tax treatment, due to the theoretical threat of loss if liquidity isn't available. I worked at a company that had this at least while I was there.

I was a regular SDE at brex for a couple years and my various documents about comp say I have RSUs, and carta says so as well.

I've never bothered to understand the details since none of the private companies I've worked for have had the non-cash portion of their comp be worth anything but $0 before.

The usual move here is "double trigger" RSUs that don't vest until a liquidity event, thus no taxes due until said liquidity event.

Nope, you as a company owner are highly motivated to shift to RSUs once you hit a certain valuation and number of employees. Everyone does it.