On the other hand, the 6th gen Mini uses an A15, and has USB 3 speeds support (only 5Gb but still).
So apple might have had USB3 speeds support in the A15 specifically for the mini, or they might have included USB3 support for a while in all SoC and enable it selectively for segmentation purposes.
That would gel with the comparison between the iPad Air 5th gen and the iPad Pro 5th gen: they both use the desktop-class M1, but the Pro supports full TB3 and USB4, while the Air only supports 10GB.
So apple might have had USB3 speeds support in the A15 specifically for the mini, or they might have included USB3 support for a while in all SoC and enable it selectively for segmentation purposes.
That would gel with the comparison between the iPad Air 5th gen and the iPad Pro 5th gen: they both use the desktop-class M1, but the Pro supports full TB3 and USB4, while the Air only supports 10GB.