It would've been better to link straight through to the whatwg/html PR, or better yet - add a summary/animation of what this feature does rather than assuming every visitor is going to be using the single browser which happens to have implemented this (very new) spec addition.
Missing function error on Firefox and Android 10
Same on Safari on iOS. It does work when I click on the inputs instead of the button above them.
I don't understand, is this surprising? The issue this post is linking to to introduce this new feature explicitly cross-references the issues for Firefox and Safari and both are still open.