Reading from a CT Sensor pin affected by Seven Segment Displays switching on and off

Other Hardware Sensors
40

If I remember correctly, you first had a 7505 and then a 12>12volt isolator in series (your diagram).
That (feeding 5volt in the 12volt isolator) won't work.
The 7805 after the 12>12volt isolator would work.

But I don't see why you want to do this.
A good quality USB charger, connected to the USB socket of the Nano, would be fine.
Don't fix problems if there aren't any. You might just introduce other problems.
Leo..