This seems to be more about knowing where people are rather than preventing them from leaving. The law in Germany dictates that nobody can be conscripted against their will. It’s a volunteer based system still.

I’m not sure how I feel about this but I am of the opinion that if a war breaks out and a service aged man escapes the country to avoid it, I don’t want them let back in once the war is over. And I’m strictrly talking about defending your own country - not attacking others. The russian who escaped the country to avoid being sent to Ukraine did the right thing. Same for any US soldiers refusing to fight in Iran.