i did some more research
got a hint from the comment section of my already posted 'Rebellion' youtube video, that a program called Blender is free and doing the exact same thing as Cinema 4D
you can download it from blender.org
next i did a search for a 3D text tutorial, found a few really bad ones and then this one:
that was a pretty frustrating experience because blender uses the weirdest menu and commands i have ever seen in a program - nothing seems to work for me, because all the usual stuff that works with windows does very little to nothing
so i recommend watching this video first, because it explains a few basics, how this program works (like pressing the mouse wheel for orbit mode):
it seems making 3D text is not very difficult once you understand how its done, and probably 1000 times better than anything you can do with any GIMP script