You might be thinking of a Warhammer mod for Tabletop Simulator.
I’m out of the loop on current happenings, but here’s an old video on how to play 9e on TTS.
Honestly when it comes to tabletop play, the rules are only a part of it. A huge part not simulated by TTS is actually building, painting, and customizing miniatures. If you want to dip into getting a few miniatures, just to feel out the painting and building process, but not buying a whole giant army, skirmish games like Kill Team or the free alternative Grimdark Firefight only need a handful of models completed in order to play.