It's a computational mode in the camera. It takes an initial photo, and then a series of photos of equal length, and composites any new light on the subsequent photos on the first. In this case, from memory, it's 5 photos at one second exposure each.
Basically, it lets you do a long exposure, without blowing out static light sources.
There's a slight post processing change to the colour, to bring out the orange/teal effect, but it's pretty subtle
Edit - FYI, your reply was tagged as German, which means that non german speakering lemmy users probably won't see it, because most instances hide replies of languages the user doesn't speak
That sounds really interesting, thank you for explaining. The last firework I tried to capture was horrible, just as you described, the static light sources blew out. Does this technique have a name I can look up? Maybe my camera has this function as well and I haven't found it yet.
And thanks for the tip with my language settings, I tried to adjust them.