You can print infinite Legos. It'll just take a high quality printer (e.g. a Prusa MK3s) and a bunch of test prints to get the tolerances right.

Now that I've got my settings for Legos dialed in I add Lego nubs to all sorts of things so you can attach regular Legos to them.

For example, I've printed a great many magnetic pins for my son's robotics team to give away as swag at competitions. They all had Lego nubs around the perimeter so the kids could attach Minifigures and other Lego parts to the pins.

Precise it is. But the hard part with any manufacturing method is tolerance or expanding/shrinking material. When you 3d print 10.85mm long bar it might actually end up as 10.88 depending on material and denseness of the print. Printing compatible Lego parts is possible, but requires some trial and error to get things right.

LEGO precision is insane. You can even tell the difference with Chinese LEPIN and original LEGO just by feel.