Using proprietary connectors.
> XHCI
Not on Lightning.
> AHCI
How exactly would Apple not support AHCI?
> Using proprietary connectors.
Not for the past decade; it's been no connectors for most products, but standard PCIe connectors for the Mac Pro, and NVMe over Thunderbolt works fine.
>> XHCI
> Not on Lightning.
Again, not relevant to any recent products. And I'm pretty sure you're misunderstanding what XHCI is if you think anything with a Lightning connector is relevant here (XHCI is not USB 3.0). You can connect a Thunderbolt dock that includes an XHCI USB host controller and it works out of the box with no further driver or software support. I assume you can do the same with a USB controller card in a Mac Pro.
>> AHCI
> How exactly would Apple not support AHCI?
This might be another case of you not understanding what you're talking about and are lost in an entirely different layer of the protocol stack. Not supporting AHCI would be easy, since they're no longer selling any products that use SATA, and PCIe SSDs that use AHCI instead of NVMe died out a decade ago. But as far as I know, a SATA controller card at the far end of a Thunderbolt link or in a Mac Pro PCIe slot should still work, if the SATA controller uses AHCI instead of something proprietary as is typical for SAS controllers.
For the same reason that Microsoft requires Windows driver signing?
Drivers run with root permissions.
Isn't that the whole point of the walled garden, that they approve things? How could they aim and realize a walled garden without making things like that have to pass through them?
Modern Mac is Macintosh descendants and by contrast PC is IBM PC descendants (their real name is technically PC-clone but because IBM PC don’t exist anymore the clone part have been scrapped).
And with Apple silicon Mac the two is again very different, for example Mac don’t use NVMe, they use just nand (their controller part is integrated in the SoC) and they don’t use UEFI or BIOS, but a combination of Boot ROM, LLB and iBoot
Because third party drivers usually are utter dogshit. That's how Apple managed to get double the battery life time even in the Intel era over comparable Windows based offerings.