"Operator '+=' is ambiguous on operands of type 'Vector3' and 'Vector2'" error even though I am only using Vector2

I searched up the problem with this error and it it apparently a problem with adding a Vector3/Vector2 to a Vector2/Vector3 (makes sense), but I did not use Vector3 here at all. What is the problem?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SquareScript : MonoBehaviour
{

    void Start()
    {
        transform.position = new Vector2(0, 0);
    }

    void Update()
    {
        transform.position += new Vector2(0, 1 / 100);
    }
}

Yes you do.

transform.position += new Vector2(0, 1 / 100);

is the same as

transform.position = transform.position + new Vector2(0, 1 / 100);

so you're adding transform.position (which is a Vector3) to the new Vector2.

transform.position is always a Vector3.

You are adding a Vector2.

For both there exists a + operator .. but not for the mixed types.

Additionally since there is implicit conversions forth and back between Vector3 and Vector2 - which btw is the reason why

transform.position = new Vector2(0, 0);

works - the compiler doesn't know whether it rather shall convert the transform.position to Vector2 and then perform a Vector2 + Vector2 operation, or whether rather convert your new Vector2 to a Vector3 and then perform a Vector3 + Vector3 operation.

That's why it says it is ambiguous.

You could of course explicitly force one conversion and do

transform.position += (Vector3) new Vector2(0, 1 / 100);

Since you only want the Y part anyway you could simply use

transform.position += new Vector3(0, 1 / 100); // equals new Vector3 (0, 1/100, 0)

or also

transform.position += Vector3.up * 1 / 100;

BUT

1/100

is also an integer division! And results in 0! You probably wanted 1f / 100f to have a float division

And finally this still would be frame rate dependent and you rather want to use * Time.deltaTime to convert into a frame rate independent value per second.