Unnecessary whitespace change here.

extract_input

Same comment as the other two nodes here:

I don't think this is quite right, the index here is the index into the mask, not the index of the index. Here's an example from the curve reverse node:

threading::parallel_for(selection.index_range(), 128, [&](IndexRange range) {
  for (const int i : range) {
    splines[selection[i]]->reverse();
  }
});

Inverting a matrix that's built from a translation is the same thing as building the matrix from the opposite of the translation, only much more expensive.

Multiplying a matrix with the identity is the same as doing nothing at all, I think the following should work here?

instance_transform = pivot_matix;
...

(Though in this case there's really no need to do the assignment.

I think multiplying a matrix by another matrix that was just built from the same as just translating matrix directly, like with add_v3_v3(transform.values[3]