The input signal selector in PPS, is a 1 out of N selector/multiplexer.
See Wikipedia: https://en.wikipedia.org/wiki/Multiplexer
Each input selector belong to a input signal of a peripheral, and can only select one signal at a time.
If you have made a mistake, or want to change a selection,
then you may click on the green 'lock' icon, to unlock the selection, and select something else.
You may select the same pin as input for another peripheral.
And you may select a pin that have been set as output for one signal, as input for another peripheral.
Such a selection will show up with a 'Chainlink' icon.
Fan-out of pin signals isn't so much of a concern with cmos logic.
Each pin have it's own output driver amplifier, so the signal passed by PPS multiplexer is only control signal,
not pin output current.
Anyway, all signals that may be selected, are permantly connected to all the multiplexer inputs that may use it,
so wether two different multiplexers select the same signal, do not matter.
Also, each pin have it's own input buffer, feeding signals to all the multiplexers that may use the signal.
There have been bugs and unnessary limitations in MCC pin setup.
Among other in connection with Oscillator pins. The crystal oscillator amplifiers for Primary crystal oscillator,
and for Secondary Crystal Oscillator, are essentially analog amplifiers with some gain control and other tricks,
and have nothing to do with digital tristate output setting.
Crystal oscillator circuits have its own control over the pin drivers,
so override eventual setup mistake made by MCC.
This seem to have become better in the latest version of MCC.