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I've have watched that video a couple of times , but not with a notion that UEFI was being chucked.
That boot process isn't iBoot. Or isn't close to what iBoot is now.
You can boot external drives. If the Apple Silicon (AS) Mac has Thunderbolt that is a wide varient of stuff ( not just USB ). SATA drives , NVMe drives , etc etc. whatever has a supported PCI-e controller. It can't be solely what the iPhones do where external boot drives don't even exist as a concept. There is an "iPhone iOS / iPad OS like security" boot path but not quite the same.
Secondly, you can turn down the security to "reduced security". That isn't what iBoot does. Maybe it will be mBoot ( or iBoot+ ). There is a substantial amount of stuff added to cover the broader ecosystem.
Furthermore, iBoot was there in the current T2 bootchain. That didn't exclude UEFI.
iBoot comes before UEFI gets started. It could be the case that Apple is skipping UEFI and bouncing directly to a small macOS instance. Mentions around the 20:16 timestamp that the new login process is a booted macOS driven password screen. ( a bit odd that can boot macOS even with Filevault on. but T2 has multiple layers of keys so it could just go grab the crypt key with no authentication. )
If there is no UEFI though that would be problematical for a boot screen for a non Apple GPU. (laptops and iGPU only systems not a big deal but that isn't the whole Mac ecosystem). For the "reduced security" path it seems there would be lots of stuff that UEFI does that they'd have to add to get coverage. But that could be just the "mac boot" fork of the bootloader. If always jumps straight from "apple boot" straight to macOS then that would be a big permanent show stopper from booting other operating systems.
It is probably not classic UEFI. ( the BIOS compatibly stuff is undoubtedly going into the garbage can. Intel is suppose to be dropping that too for newest systems around this time. )