I’ve added an official shadow catcher functionality to the engine, which should come out hopefully this week: Shadow catcher shader support + script + example by mvaligursky · Pull Request #7426 · playcanvas/engine · GitHub
but there is this script which has a very similar functionality that you can use, it’s not limited to AR: web-components/examples/assets/scripts/shadow-catcher.mjs at main · playcanvas/web-components · GitHub