Does it work using Safari for iOS?
And in case you have a webview application to check, does it work using WKWebView?

If it works in the former and not in the latter, it is a WKWebView bug and you can file a Radar issue with Apple.

Yes, it works using Safari for iOS, the input change is triggered. I don't have any webview application to check that, but I uploaded the form on this URL: martar.fr/demo-chrome.html 

How could I easily check if this is due to WKWebView? 

Firefox seems to be using WKWebView, so if you can reproduce using Firefox, that would probably prove it.

And you probably meant "the 'input' event is triggered" instead of "the input change is triggered". :)

Yes, that was indeed what I wanted to write, but we can't edit our comments :)

I tried on Firefox but I fail in saving an email into the browser so I can't reproduce the issue..

I forgot the automatic completion is a Chrome feature and not a WKWebView feature.
Here is the code -
https://cs.chromium.org/chromium/src/ios/web/web_state/js/resources/common.js?q=_gCr&sq=package:chromium&dr=C&l=258
It simply fires the "change" event and nothing else.

Ok thank you! So do you think that this should be changed, or web apps should adapt to this behaviour? 

It seems like a bug to me, but I am a user just like you. :)
The team will decide whether this needs to be fixed.

 Issue 813175  has been merged into this issue.

Fixed with https://chromium-review.googlesource.com/c/chromium/src/+/771674