This is a very complex question to ask.

Warning: Its not able to not oversimplify this answer.

At which point is a denazification successful or effective?

To make it short:

Through the economic growth and the financial help of the USA, the denazification was highly effective. Keep in mind that the Germans had a mentality of obligation to rebuild their country.

Now look at the generations:

1. The generation who survived the war as adults were more likely to deny the fact that the Nazis did something wrong. They felt wrongfully treated but on a higher level. Imagine: Growing up in poverty, hunger, WW1 and a psychological unhealthy enviroment. Before the raise of the Nazis, there were political murders everyday. The Germans were sick of it and had to choose between Hitler or Thälmann (Stalin friendly communist) to end this situation. Anti-semitism is a topic for itself, I dont want to treat it oversimplified. Thats why I leave it out. In general, this generation would rarely talk about the Nazis in public. It was a tabu. Nethertheless, you will find many Ex-Nazis in political positions during the 50s. The Nazi supporting nobility kept silence, too. But this generation highly supported the right to arm oneself to prohibit the next dictaturship.

2. The generation, who survived WW2 as teenagers or kdis, had to face diffrent identification problems. At some point, there were patriotic but they had to deal with a huge amount of guilt, shame and rehabilitation. But on the other hand, they lived trough the economic growth and could emancipate again. When you read novels about this generation, you will notice a weird tension. Somehow there was a atmosphere of departure but a feeling of treated unfairly by the allies; like a child, who wants to play with the older brothers but its not taken seriously. From this generation you would often hear sentences like "Hitler would not allow this to happen!" when watching the news. They have (or had) a high interet in prepping and gun rights. Even though many of them werent able to say that Hitler was completly wrong, they created a political climate to prohibit a dictatorship, too.

3. The generation born in the 60s-70s worked the hardest to heal the relationship between the Germans and their past. Many of them are pacifists and support gun ban. Rarely, you will find glowing patriots. It was also the generation, who had to deal with traumatized parents.

Nowadays, it starts to be acceptable to be a patriotic German again. On the other hand, right movements are gaining more power in Germany and partly they contain weird people. There is a significant group of Germans, who felt like the allies stole our German identity with the denazification. And then there is a significant group of Germans, who call themselves "Anti-Deutsche". They want to destroy the German spirit and say that everything German doesnt deserve to live. Germans have to be neutral Europeans.

The problem with the denazification is that the raise of the Nazis is the result of complex psychological problems of the Germans. These problems have a long history and of course, the denazification was foredoomed at some point. Which you can see now.

Please keep in mind that the raise of the Nazis is the product of a more than 200yo history and I didnt mention many important aspects + keep in mind that Germany is a connection between tiny countries, duchies and so on. Every region has a diffrent story because of many other reasons.