[JonathonW]

The A17 Pro (originally in the iPhone 15 Pro; now also in the iPad Mini) and A18 Pro (currently only in the iPhone 16 Pro) are the only chips Apple has produced with a "Pro" suffix.

Apple used to use the X suffix for bigger versions of their phone processors that went into iPads (starting with the A5X); that went away when the M-series was introduced.

And the "Pro" suffix itself doesn't seem to denote anything in particular-- there was never a non-Pro A17, and the "A17 Pro" going into the iPad Mini is itself a cut-down version of the chip that went into the iPhone 15 Pro (it has one GPU core disabled).