I have recently noticed that during my experience with foreskin restoration.

I am producing "pre-cum," whereas I wasn't before. It is common that circumcised males do not produce "pre-cum"?

No, there's no connection between a guy's circumcision status and his tendency to produce pre-ejaculate (a.k.a. Cowper's gland secretion). Some guys produce a lot of it, some only a little, and some none at all. I have no idea why you're producing more now; maybe it has something to do with the extra stimulation that your restoration project is giving you.