This is not cosmetic. You have shards of glass coming off where your food is being cooked. There are a lot of threads on here about blue interior enamel chipping on many brands of ovens. It happens less frequently with black. I would ask to have the liner to replaced.

Quick update in case anyone else experiences this issue- finally able to get an actual Bosch rep out to look at the oven. He quickly agreed this is a manufacturing defect in which the enamel coating did not adhere to the oven liner during the ‘baking‘ process. Perhaps cosmetic in terms of function, but a defect in the finish nonetheless for a fairly expensive range. Hopefully will be replaced after review by the higher ups.

I have had my oven for 5 years and just noticing the same thing - it turns out I should not have used aluminum foil on the bottom. I tried it a few times when cooking pizza. It has ruined the bottom and I keep reading that it will not harm anything but I found the thinest dark blue like shards on the top of the inside of oven when cleaning. I am very concerned for safety at this point and researching further. The little shards were thin as possible - thinner than a hair but about 1/8th of an inch wide.