The number of apples divided by the kilogram of oranges I have is a meaningless comparison and makes no sense, though.

The root of good faith conversation is that we don't latch on fuzzy meanings of words like "comparison" but try to understand which precise meaning should apply.

The result of subtraction is a difference. In my mind this is the most basic way to compare things. Subtraction of differing units is illegal.

The result of division is a quotient (day to day we say ratio). Division of different units is legal but not always practical.

Re: your deleted apples and oranges comments;

These aren't pure dimensionless numbers, they come with units of measure attached.

If there's need for good scalar try: https://en.wikipedia.org/wiki/Dimensional_analysis for https://www.sciencedirect.com/topics/chemistry/dimensionless...