There's no exception for hate speech, but there are narrow exceptions for threats and incitement to criminal activity, so particularly vicious hate speech is sometimes found illegal for those reasons.
I guess depending on the context, that could be applied to displaying Nazi flags.
This one's kinda close:
https://mtsu.edu/first-amendment/art...rginia-v-black
That's the USA. Finland is just a little stricter: it's also illegal to "promote discrimination against ethnic groups", so while Nazi symbols are not banned, you can easily commit a crime by displaying them...though the punishments tend to be light.
Canada, Western Europe, and obviously Germany have even less tolerance for such things.