This Doc works fine but need to keep three important configuration in mind that are not mentioned in the doc.
Administration -> General -> Macros -> add {$ZABBIX.URL} = http://DNSNAME/zabbix/ You Must Get Zabbix UI
Enable Configuration -> Actions -> Trigger actions -> Report problems to Zabbix administrators
You can send alerts via Admin user too.
Administration -> Users -> Admin -> Media -> Type (MS Teams) -> Send to (MS team connector) -> update
I tried on Zabbix 5.2.6 Follow This Doc Link for more details