That’s tiny, more of the size they put on under the desk exercise bikes or a childs bike not a normal upright bicycle. That means your feet are spinning in tiny circles and are not getting the proper range of motion in the knee even if the seat height works for you. For comparison a normal a mans mountain bike will normally come with 175mm …
https://www.amazon.com/Marcy-Exercise-Magnetic-Resistance-NS-654/dp/B01N6I3HPJ