Facebook doesn't really decide what you see, but instead optimizes what you see to maximize your engagement. If you never engage with political content or misinformation, you generally won't see it. Once you start engaging, it will drown out everything. What they could provide is a "no politics" option, but I wonder if anyone would utilize it. There was an old saying in the personalized recommendations world along the lines of "if you want to figure out what someone wants to read, don't ask them because they will lie." For instance, if you ask people what kinds of news they want they will invariably check "science" but in fact they will mostly read celebrity gossip and sports.
Facebook decides what you see. That they have created an algorithm that "maximizes engagement" is just another way of saying that they've decided what you should see is what they believe will keep you most "engaged". They could choose to use a different metric -- it is entirely their choice.
Facebook as experimented with a number of different options to clean your feed but ultimately they never get deployed because they all decrease engagement.
