The only available specification is typical (not guaranteed) input capacitance 20pF on all PIXI ports, regardless of configured mode.
When configured in mode 1100 Mode 12: Terminal to register-controlled analog switch, two adjacent PIXI port pins are always connected together, and there is only the 20pF typical load capacitance on both of the pins (so a total of 40pF typical).
When configured in mode 1011 Mode 11: Terminal to GPI-controlled analog switch, two adjacent PIXI port pins are controlled by another GPI configured pin. The datasheet does not specify the off-capacitance between the two configured PIXI port pins when in the off (disconnected) state, nor is that a tested nor guaranteed parameter. We don’t even have a typical value for the off capacitance.