Just as air filters are not polluting the air with massive clouds of nanoparticles your face mask is not filling your lungs with them.
The vast majority of what you interact with is made of plastic, at least the mask is useful
Pick your battles. First you don't want to be sick/die/cause your elder relative to die by infecting them. Then once you are not dead you don't want to get into your body substances that clearly have no business being there and can make you sick slower and less noticeably.
I'm guessing you would want to run a filter/wear a mask if there's a good reason and not do it when there isn't.
Seriously - if I had enough tinfoil - I'd say that our entire dietary ecosystem is under attack, directly, in order to reduce the healthiness of our food supply. Plus the many many food processing/farm etc plants which caught fire in the last 18 months.