We will want to update at least IE 11 in https://github.com/matomo-org/matomo/blob/4.x-dev/core/SupportedBrowser.php#L30-L37

Likely other browser versions increased as well.

Even though we are dropping support for IE 11 before Matomo 5 we will likely wait for this specific change until Matomo 5.0 as otherwise the UI won't be accessible using IE 11 anymore at all even though parts could still work