Is it possible to calculate and unknown point on an EC

I aim to find the answer to what is $X$ on an EC over a finite field where $A + X = B$ and $A$ and $B$ are known. I’m currently learning with secp256k1 so the simplified equation for the curve is $y^2 = x^3 + 7$. I am trying to figure this out so I can write the formula in python.

Since an Elliptic Curve is a group, $A+X=B$ in this group can¹ be solved per $X=(-A)+B$, where $+$ is the group law and $-A$ is the opposite of $A$ in the group.

To compute $-A$, change $A=(x,y)$ to $-A=(x,p-y)$. The addition formulas are in Sec1 §2.2.1. If you get $A$ or $B$ in bytestring form (perhaps, compressed), use the conversion in Sec1 §2.3.4. The value of $p$ for secp256k1 is in Sec2 §2.4.

¹ _{Proof: $A$ is a member of the group, thus has an opposite $-A$. We add it on the left of both sides of $A+X=B$, yielding $(-A)+(A+X)=(-A)+B$. We use the group law's associativity to get $((-A)+A)+X=(-A)+B$. By definition of the opposite, $(-A)+A$ is the neutral $\mathcal O$, thus $\mathcal O+X=(-A)+B$. By definition of the neutral, $\mathcal O+X=X$, thus by replacement we get $A+X=B\implies X=(-A)+B$. Proving that $X=(-A)+B\implies A+X=B$ is just as easy, by adding $A$ on the left of both sides.}