I turned off Autofill in Chrome, and it still seems to do it.
An example I’m used to is the Woocommerce ecommerce plugin. In Woocoommerce > Settings > General you can choose what countries to ship to. As you start typing it presents a list of matches. You can then scroll down with the arrow keys and make a selection with the Enter key. It then populates the text box with that selection and lets you choose another.
If you wanted to play with it to maybe divine how they’re doing it, and don’t have or want Woocommerce installed, I could give you a login to my testing site.
Thanks