The chances of the Asus ZenFone 5 getting updated to Android 10 seem to be slim if the tweets of an Asus France employee are anything to go by. In a response to user's query, the rep said that a lot of work needs to be done before the update can be made available for the ZenFone 5 considering the fact that it is based on ZenUI, and that it runs on a different chipset compared to the ZenFone 5Z, which has already received Android 10.
https://www.notebookcheck.net/Employee-s-tweet-leaves-Asus-ZenFone-5-Android-10-update-prospects-hanging-in-the-air.453520.0.html