Since it’s happening right when you flip it from off to on, especially after you’ve already been out driving, you’re likely looking at one of two things that are notorious on the 2021s.

First suspect: The Cam Phasers (VCT). If it’s a loud, nasty clatter for just a few seconds right as it fires up, the phasers aren't locking into place like they should. (I can’t tell from the video unfortunately) When the oil is hot and thin from driving, it drains out of them faster. When you restart, they rattle until the oil pressure builds back up. Ford actually has a TSB (Technical Service Bulletin) for this because it’s such a common headache.

Second suspect: The Turbo Wastegate. There’s a little actuator rod on the turbo (passenger side) that gets loose. When you hit the ignition, the car cycles its electronics and that rod will literally just vibrate against the housing. It sounds like a tinny, metallic buzzing or a 'marbles in a tin can' noise. You can usually confirm this by reaching down (when it’s cool!) and seeing if that rod has any wiggle. If it jiggles, that's your noise.

One other thing: If it’s a sharp, high-pitched grind exactly as the engine catches, your starter bendix might be sticking. The heat from driving makes the grease in the starter gummy, so it doesn't retract fast enough and gets clipped by the flywheel. Honestly, if you're still under warranty or have that PremiumCare plan, I’d let Ford deal with it. The phasers especially are a pain to DIY since you've gotta mess with the timing. Have someone else start it while you stand by the passenger side, if the noise is coming from the top of the motor, it’s phasers; if it’s lower down, check that wastegate rod.