No I didn’t. Have a read of what I said.
The Vin line on an Arduino Uno is connected through a series diode to the input of the regulator. This diode drops 0.7V so if you connect 5V to the Vin it will put 4,3V onto the input of a 5V regulator. So the output of that regulator is going to be something in the order of 2.8V which you then propose to connect to 5V. This is all screwed up.
You only ever have a common ground, you never have both the ground and supply connected to two power sources because they start to fight each other. Leading to currents going in all sorts of directions.