Enabling webgl 2

This is something simple, but I can’t find how to do this. When packaging for html5, I’m getting errors suggesting that Unreal packages with ES2, i.e. using webgl1. I would like to use the ES3 features.

How do I enable it when packaging to html5?
As far as I understand, ES3 is supported since UE 4.16 and ZenGarden demo was built using it. I thought I’ll check how the demo was packaged, but the package on marketplace doesn’t have html5 support.

How to do this? Thank you!