> Only when threatened and self-defense has to be proportionate. If someone attacks you with a knife you would not be allowed to defend yourself with a firearm if you had one.

No, that's explicitly not the case, it doesn't has to be proportionate, only needs to be the mildest defence available to you that will stop the attack.

Not sure where people get the idea that the defense has to be proportionate, for some reason many believe that.

Defending yourself with a gun against an attacker with a knife is well within your rights (assuming that drawing and defending with a gun would even be effective).

See here for example as reference: https://zjs-online.com/dat/artikel/2020_2_1383.pdf

First 1-2 sentences.

"First 1-2 sentences"

First sentence is "Zur Erforderlichkeit der Notwehrhandlung" (About the necessity of self defense acts).

The whole document is about the necessity aspect but §32 StGB requires Notendigkeit (necessity) AND Gebotenheit (appropriateness).