Only the General Test, as far as I am aware, because far more people take this test compared to the subject tests. Subject tests are more specialized, similar to what the SAT Subject Tests used to be. Therefore, there are fewer people taking each specific subject test and not so much a need to provide an at-home testing option.
Maybe ETS might make such an option in the future, but the way the COVID pandemic is now (which resulted in the creation of the at-home option in the first place), the trend of making GRE's in general optional at some departments, and the array of (technical) problems that can arise with the at-home testing, it doesn't seem that they will be able to justify doing so any time soon.