We are able to confirm that Dying Light 2 will not support crossplay across other platforms or console families. As a result, you will only be able to play the game with other people who have it on the same platform or console family as you do.
I want to say it's one to one, but in all honesty I'm a bit fuzzy there. I can recommend JoyFreak's sister site AdminIntel - Admin & Webmaster Resource where there are lots for people of varying degrees of expertise with development, you likely can get a far more precise answer there!