I’m still wanting to make a real post but until then, is it just me or is it supposed to be r2 not d2?
It can be either, as long as you know what it stands for, and I have seen it presented in many ways.
Some people use r for radius as that works nicely for an orbit and is consistent with F=m omega^2 r=m v^2/r.
Others use d for distance, sometimes to not confuse it with the radius of the object.
What is important is the meaning, not the variables used to represent them.
And if you want to get into the more technical level of how to represent them, as they represent physical quantities they should be in italic font, and then because they are both masses, both should be represented by a lowercase, italic m, with superscripts to distinguish between them.
e.g.
F =
G m1 m2 /
r2