This is not my experience as a person involved in hiring in Europe.
If you never stay somewhere more than a year it’s a red flag.
If it’s less than 6months then you won’t pass the HR filter.
My suggestion is that you shouldn't wait very long at all for an internal promotion if you can just get a new job that pays better. I can't imagine this is a process that you engage too much in in the first year of a job, where you likely wouldn't be eligible for a promotion in the first place.
At least for me frequently is 1-3 years while i do wanna know why you left your company after a year.
But it is easy to come up with a reason why you switched early and in this market, i take one person who swtiched early but feels like a good candidate over one who feels like a bad one.
The market in germany was empty the last 5 years, we were happy to get what we could.