Nothing is ever just a matter of mass production. Scaling brings its own, massive problems, some of which Tesla experienced with the relatively simple Model 3.
You're right, scaling is another topic. If you can produce 5 prototypes you can produce 500 of them. Making that happen at scale in a timely manner requires introduction of automation, assembly lines, humans, checks and so forth. However, I argue beyond being laborious it's not any sort of impossibility as compared to something like FSD.