connect pi picos together with gpio?

Is there a way to have the output of one pico set off a gpio of another one without damaging either? I'm thinking the output of pico A sets off. GPIO #1 of pico B (where A is an output and B is an input)

Yes, if they share the same ground (GND) that is not a problem.

So the same ground as in just one ground needs to be connected in each and im good? All the grounds? Or every single used ground?

One GND from Pico 1 needs to to be connected to one GND on Pico 2. There are several GND pins on a Pico and they all have the same electrical potential, Zero volt or Ground.

Cool. One gnd to each. Thank you!