According to a ZenTalk forum moderator, Android 10 will be the last major OS update for the popular Asus ZenFone 5/5Z. Further updates will only focus on security and bug fixes, although the possibility of a ZenUI 7 feature update for Android 10 is not being completely ruled out.
https://www.notebookcheck.net/Android-10-will-be-last-major-OS-update-for-the-Asus-ZenFone-5Z-but-possibility-of-ZenUI-7-is-not-being-ruled-out.461658.0.html