Even though I am not the answer provider you wanted, I would like to attempt an answer.
The topic is certainly very diverse and complex and very difficult to summarize in a few sentences. One can only touch upon it.
It starts with demographics, education, etc. Decades ago, there was an attempt to solve the emerging demographic catastrophe with immigration. A failed family policy with today’s dozens of genders speaks a clear language. We lack offspring. Well-educated youth can no longer be found; instead, there are youths unwilling to integrate who live in parallel societies.
An ever-flattening educational level has accelerated the decline. Key industries were lost and where Germany lost its leading market position in many areas. 95 percent of students with a migration background in Berlin schools. Districts in West German metropolises with 70 - 80 percent migration share.
All this is associated with extreme costs borne on the backs of the wage earners, with ever-increasing burdens up to the minimization of the middle class. Lowest pension levels and home ownership in the EU. Although the strongest economic nation in the EU, we have the lowest median wealth.
The Bundeswehr, the infrastructure, the healthcare system, the education system have all been ruined by austerity measures.
And now, where various wars are raging, Germany is the largest arms supplier. Both to Ukraine and to Israel. All with money we don’t have.
I don’t want to elaborate on this any further.