We upgraded our zabbix monitoring from Zabbix 3.4 to Zabbix 5.0.41 but upon creation of the platform we got an error message saying that MySQL: Failed to get items (no data for 30m)

Also, we are trying to monitor other servers in our organization but the auto - registration is not detecting. We installed the zabbix agent that we got from the download platform then copied the configuration of the zabbix server to the zabbix agent installer but upon installation we cant connect to the servers and the latest data is not reflecting and we even got further error detected.