Let's tackle this question first, "So, I'm wondering ... is the airway-clearance which is so much being talked about here, importantant only for NTM or also for "normal" European
bronchiectasis?"

Airway clearance is important in bronchiectasis to help prevent NTM, pseudomonas, or any of the other infections that like to inhabit compromised lungs. In fact, although it was first practiced mainly in Cystic Fibrosis patients, and more recently in Bronchiectasis patients, pulmonologists are beginning to realize it is effective for people with COPD as well. See this informative Webinar by a world expert in NTM/Bronchiectasis:

Next, let's talk about "so, this terminology exists in USA , where NTM (non-tuberculous microbacteria) is so common. It's not really bronchiectasis, which is a widening of the bronchii. It's more like a classifiction of NTM, which often leads to bronchiectasis."

While it is true that not every person with NTM has Bronchiectasis, most have it or COPD. To be clear, NTM is NOT as USA disease - it exists worldwide. Until recently, and maybe even today, it is underdiagnosed because it is rare - fewer than 1 in 1000 people has it in the US, and it looks like many other lung infections. Here is a report looking at global studies of NTM:
https://pmc.ncbi.nlm.nih.gov/articles/PMC6670190/
Usually people are treated repeatedly with antibiotics for pneumonia or bronchitis, often until a sharp-eyed radiologist sees evidence of NTM or bronchiectasis on an x-ray and the proper tests are done to reach a correct diagnosis. As Europe and Asia "catch up" to the US in recognizing the symptoms and doing lab testing, it is expected their rates will be similar to the USA and Canada.

Finally, it doesn't matter whether the disease is described as nodular NTM, cavitary NTM or Bronchiectasis, we are here to talk about the best way to manage it, to live our best possible lives in spite of it.

Have you been diagnosed with NTM, Bronchiectasis or both? Did you ever find an expert pulmonologist to treat you in Germany or nearby?