At most companies your direct manager can't fire you either. They simply write reviews and escalate problems to upper management/executives/HR, who then decide whether to act on it or not.
Well, no but that's mainly because of asymmetric numbers.
If all reports of a manager complain to the managers manager, that manager will likely be reassigned or reprimanded in a similar manner to a manager and an IC.
Also I should note that in most of Europe (at least the parts I've worked in), a managers voice is just a louder voice in a room of other managers- and firing someone is something that is not done by an individual, it's a discussion with managers and HR.
It's not taken lightly to fire people, even in places that are "at will" (theoretically) like Denmark.
Depends on the company but I'd say in most small and medium-sized companies in the US, your manager can fire you without cause and be just fine with maybe some half-assed explanation if upper management asks questions.
