RSI got back to me. Harnesses for incandescent tail lights are on their way to Texas and will be shipped out when they get there. Harnesses for LED tail lights on still in development with no current ETA, but there is a waitlist. Contact support if you need one.
That was my next step. I'll let everyone know what they say. The box had a big sticker on it "wiring harness not included." Not sure if there was a supply issue, or if they aren't including one with the 2021's.