And be able to rotate/scale afterwards. Please note that this should work with multiple objects placed on the floor, so I need to be able to detect a tap on a placed object to decide that that will be the object to rotate and scale.
See video as an example
cc @RaananW
Of course, this is what hit test is for 
(among other things)
All of our hit test demos do exactly that - place an object on the floor. For example:
See here - WebXR Augmented Reality Features | Babylon.js Documentation
On this example there’s a torus that follows the camera but you can never place it on the floor or do anything else.
have you tried clicking on your screen?
Also, some demos require the webxr incubation flag in chrome://flags . Hit Testing alone is a part of the stable API so no need for it if all you want is hit testing.
Hello @marcusx2 just checking in, was your question answered?