Oh I see the original syntax was like: 
Sadly I can’t edit my post.
I strangely noticed that some images were converted to the following format: <img title="" src="file:///home/felix/Documents/WS21-22-Repo/Grundlagen%20der%20Signalverarbeitung%20und%20des%20machinellen%20Lernens/assets/2022-02-09-12-55-16-image.png" alt="" data-align="inline">
it is working when I add the file tag! thanks! the /// is not necessary in my case.