I was also looking into it, but the initial maintainer of this app has stopped working on it. So we need to find someone with time and abilities to upgrade the app.
Actually there is work for last Zabbix version, on another PR : Version 6.4 by lapineige · Pull Request #46 · YunoHost-Apps/zabbix_ynh · GitHub
But keep in mind that all of this relies only on unpaid work from 
amazing vonlunteers 
from our community 