Like just about everything else in the EU pre-Disney, yes. But technically, unless directly contradicted it still exists in a nebulous quasi-canon state (High Republic takes place a couple of centuries before the prequels, Old Republic was about 3000 years earlier), and current authors can take stuff from it for their own works.
However, there is a remake of the original Knights of the Old Republic game supposedly in the works that would presumably be nu-canon.