In Zabbix 6.4 items can have ZBX_NOTSUPPORTED only in case of misconfiguration, like:
1. Incorrect item key
2. Missing log file
3. Timeout related to slow item key execution on Zabbix agent side
and etc.

Now ZBX_UNSUPPORTED can be for network issues related to general communication with Zabbix agent:
1. Connection refused
2. Permission denied for Zabbix server / proxy

Finally all passive Zabbix agent items can be unsupported, while Zabbix agent just is not available at all.

Such behaviour can have the following problems:
1. Incorrect actions for internal events
2. Confusing with amount of unsupported items (internal item)
3. Difficult to find real issues with such items

Additionally if remote Zabbix agent does not allow Zabbix server IP address (different IP address in Server parameter) the current message does not show real reason: "Get value from agent failed during receive: timed out", while before Zabbix shows "Check access restrictions in Zabbix agent configuration" message.