No alarm when zabbix loses its active proxy

[Spectator]

There is an active proxy with "Template OS Linux by Zabbix agent active" and "Template App Zabbix Proxy" templates.
If the Zabbix server loses connection to this proxy, I will not receive any alert.
This is normal? What can I do?
There is one such trigger in the "Template OS Linux by Zabbix agent active" template - which I think should alert you: "Zabbix agent is not available (or nodata for {$ AGENT.NODATA_TIMEOUT})"

On the zabbix server, I use the following iptables command to disconnect from the proxy for the sake of the test:
iptables -I INPUT -s xxx.xxx.xxx.xxx -j DROP
(xxx.xxx.xxx.xxx is the IP address of the proxy)

The Zabbix (and proxy) version is 5.0.17 LTS

This templates are linked to the proxy:
Template App Zabbix Proxy, Template OS Linux by Zabbix agent active (Template Module Linux block devices by Zabbix agent active, Template Module Linux CPU by Zabbix agent active, Template Module Linux filesystems by Zabbix agent active, Template Module Linux generic by Zabbix agent active, Template Module Linux memory by Zabbix agent active, Template Module Linux network interfaces by Zabbix agent active, Template Module Zabbix agent active)

Does anyone have any idea what the problem might be? Or is this normal?

[Spectator]

Agent and proxy are a bit different things, I think..

You can have items for that on your Server
Type: internal:
Key: zabbix[proxy,<proxy>,lastaccess]
interval 1m
trigger: key.fuzzytime(300)}=0 (proxy has not been seen for 5 minutes)

Thank you.
I will try next week.