How do you trade with unsettled funds correctly in a margin account?

Pretty much, I tried before but I got hit with a free-riding violation. Well the 90 day temporary cash restriction comes off tomorrow and I'm ready to jump back in, but I want to do it correctly.

I understand how I got the violation, because I was going all in on an etf, sold when it went up and jumped right back, bought it when it dropped later in the day, sold it went up again and kept doing the process, because it said my buying power was reset.

Apparently, you can't do this.. even though I thought the built-in mechanics would have stopped me from buying another etf if it wasn't allowed. (Beginners mistake)

Let's say I have $20,000 in cash and tomorrow I decide to put $19,999 into Micron... Micron goes up and I pocket the profits and all of a sudden I have $20,500 in unsettled funds.

Am I correct in that I can now trade again with the $20,500 unsettled and not have to wait to the overnight reset as long as I don't buy etfs like spy, voo, etc..?

I want to hear from people who trade on Fidelity with unsettled funds multiple times a day please and have experience with this.