is it possible to fly to Ukraine and join their military in support of opposing Russian influence? That or join a militia group there

I speak and read Polish, so learning Ukranian should not be a stretch.
I am relatively skinny, but I am fit from running.

inb4 >war is bad you dont understand
the challenges that modern society provides are a joke, if you are not escaping it then you are doomed to succumb to it.

I have purpose at home, I know I should not take it for granted. War is not appealing to me, but it is the ultimate inevitability

How achievable is this?