What are the potentials on the Arduino analog inputs?

Question

Arduino

I ran into an incomprehensible problem: there are some incomprehensible potentials at the Arduino analog inputs that interfere with measurements. And at different entrances - different and even "walking".
Question: what are these potentials and where did they come from?
Tried digitalWrite(54, LOW); - does not work.
And in general, it is not clear in principle what kind of voltage it is. In no place on the Internet have I found any mention of either voltage, or the problem of displacement of the measured value, or the need for an additional resistor pulling it to ground. Yes, it is useless, given the "walk" of the offset.
What is it at all (and how to remove it)?

Scheme of the experiment The

question is removed. Thanks to all who answered - if I find a solution - I'll unsubscribe here.

Answer 1

If these are inputs, why the hell do they do digitalWrite? Or is it still the way out? :)
And the wires hanging in the air will catch incomprehensible pickups until you pull them to the ground, this is the norm.

Answer 2

Please provide the experimental design.
Or do you just do it on the board, and did not connect anything to the inputs?
If yes, get just that - the weather on Mars.

Answer 3

It can be assumed that something in the code made these inputs discrete and turned on the pull-up resistors to the plus, since they all have a high value (from 696 to 1023).
Although I can't say for sure because I haven't experienced it myself.
(no pullup lines anywhere in the code?)

Answer 4

On the Mega, the inputs are connected and measure currents and voltages. On the Duya, they hang. This does not affect the potentials in any way - this can be seen in the screenshots.
Scheme of the experiment
Everything is as in the picture, only I have a plus offset