I also looked for another issue mentioning Hand-tracking but couldn’t find it. I added it as a list item in #6958 - WebXR Improvements so it is consolidated.
First, I think you are going to need BJS 5.0 alpha, even though it was on 4.2. The API for hand tracking changed a little after 4.2 was released, but a little is all it takes when it comes to APIs.
I think there are a couple of PG’s in the hand tracking Documentation. Do not think there is one for touching 3D buttons yet though. I made no PG’s, & am not happy right now with my current work to actually point someone to it.
If you searched out the docs, you would see some some key search functions to find others people PGs. Good hunting.