Is it normal for PhD students to do much "non research" work? Background: At my current institution I haven't even officially started my PhD yet, meaning I am not even enlisted as a PhD student. I have my bachelor’s and master’s already, and this is in Germany so “thesis only”. I also have worked here for a while now during my master’s so I know the institute well and they also know me well, which may be part of the problem as I am not “just a PhD student”.

The problem is that I get buried in all kinds of work like,


writing parts of grant proposals (many, not one or two like other questions mention)
giving popular science talks about our work on any given chance
presenting our work during lab tours for all kinds of guests (which happens often)
writing news articles and marketing material
supervising students and assistants
...


It’s not that I don’t like doing that stuff as much of it helps me to improve my writing, presentation and people skills.

My problem is that there is nearly no time left to actually do research. I just present old stuff or the work of colleagues that is to some degree build upon my old stuff. I feel like I do the work of a postdoc or professor and not the work of someone that hasn’t even started their PhD yet.

So to what degree/amount are the mentioned tasks normal for a student in my stage?
These all sound to me like usual activities for a PhD student (the "news articles and marketing material" bit sounds a bit odd to me, but that might be more field-dependent).

PhD programs are not typically designed only to allow you to do research, they are designed to teach you to do research, and furthermore to train you to be an independent researcher. That can include learning about all the other baggage that comes with research, such as finding funding, disseminating the research to the academic and sometimes lay community, mentoring junior researchers, etc. 

However, like most things, balance is important. It's hard to specify some number of hours per week or something like that for you to contribute to these "other" activities, but the most important thing is that you are able to make progress in your research.

Since your advisor will be the person judging your satisfactory progress as well as being the person assigning you all these tasks, you should have regular conversations with them as a student regarding this balance. Have these conversations early and as often as necessary. It would be appropriate to approach this question directly as you have asked it here, too: tell your advisor "I am worried too much of my time is being spent on X/Y/Z and it will be difficult for me to make progress towards my thesis."