I had spinal bifida, but it was corrected and cap is missing from my lower backbone. should i abstain from heavy weight lifting or just from squats?

No: There is no reason to believe you can't weight train. Obviously if it hurts when you do it then make sure you have proper guidance for lifting.

Spina bifida: I would get a consultation from a pediatric neurosurgeon to see how severe the disorder is or was and based on the present findings you will get a better assessment of what you can and cannot do.