Hi, I can't help you, but I can confirm that tutorial #3 is broken in the latest version 1.12.2. The problem exists both in the German and English versions.
This tutorial is called "Bauen für Fortgeschrittene" in German ("intermediate construction" in English).
It starts with opening the spaceship called "Hüpfer" (Hopper), which doesn't exist. I opened "Springender Floh" (Jumping Flea) instead, which seems to be roughly the same.
After adding a few elements until five FL-T100 fuel tanks, you are supposed to add a "Triebwerk" (engine) named LV-T45 "Schwenker" (Swivel) but the tab "Triebwerke" (Engines) is empty.
So there is no way to proceed and complete the tutorial.
That's obviously a bug.