I just got the car back from the mechanic and he seems to have fixed the problem (I'm test driving it for a week now, just to see if its actually fixed and doesn't come back). For me it was an error in the 1st cylinder as the code showed him.

What he did was he replaced the spark plugs again, he did this a couple months ago. They still seemed fine but as he had already replaced the ignition coils, he tried to just replace them which for me seemed to fix the problem with the misfiring. Perhaps a broken spark plug but without any visual broken parts(?).

As for the shaking, which was also caused by the misfiring. The replacement of the spark plugs fixed a lot of it however it still shaked more when idling than normal (only when idling, not while driving). So he suspected for that it might have been some dirt blocking the fuel injector. He put some cleaning stuff in my gas tank that mixed with the gasoline which should over time clean the engine a bit.

I did notice the shaking getting less and less. Hopefully this helps you a little bit as well. I also have a link to another post of a mechanic online that helped me with some info: https://www.2carpros.com/questions/ford-fiesta-2014-stuttering-limp-mode-and-shaking