Hi Jerome,
Thank you for the details, I logged in to check.
There should be a Choose button visible, but it is forcefully hidden via a theme stylesheet file originating from the “nectar addons” directory. It should not be loaded on this page, but sometimes developers forgot to exclude their files, or have other reasons to load them anyways.
I went ahead and made a modification to the plugin stylesheets to forcefully override this for the search backend. I think we can include this in the next patch.
If you clear your browser cache, then it should start working.