How important is specialisation in a master's degree?
I can just answer your question from the industry side:

I know enough people that don't even work in the field where they studied. Here in my department (in a well known company) we have guys from computer science, engineering and electrical engineering working on the same tasks. It's more important to have a technical degree than have a good specialization. Most of the hard skills you need for your work aren't taught in university. The important skills are the soft skills that the job will give you (to complete in stem fields with good grades will show them that you are not totally dumb and have the stamina for hard tasks).

Visit the courses that sound useful to you. I did it that way and am completely happy with my decision.