Same - I wonder if it's because it's some sandbox context and it's trying to bind to window (it's the UMD version)
It looks like the reason it doesn't work here is because it relies on "this" being the window object. To make top-level await possible your code gets wrapped into a function, and in there "this" no longer points to the window. I am sure a workaround is possible, I'll make a ticket on github.