PSA - the main ideas behind “causal ML” and “double machine learning” go back at least 40 years
Here is an estimator from a 1982 textbook that today would be called double machine learning or something similar
Once you have a pathwise differentiable parameter, a natural estimator is a debiased plug-in, which subtracts off the avg of estimated influence fn
Pfanzagl gives this 1-step estimator here - in causal inference this is exactly the doubly robust / DML estimator you know & love!