https://www.zabbix.com/documentation/6.2/en/manual/api/reference/hostinterface (Zabbix 6.2 API documentation) says about Host interface API: "This functionality is deprecated and will be removed in upcoming versions."

Zabbix 6.0 API documentation does not say that, so the deprecation appeared in 6.2.

Where is that deprecation announced? Checked:

• https://www.zabbix.com/documentation/6.2/en/manual/api/changes_6.0_-_6.2
• https://www.zabbix.com/documentation/6.2/en/manual/api/changes_6.2
• https://www.zabbix.com/documentation/6.2/en/manual/installation/upgrade_notes_620
• https://www.zabbix.com/documentation/6.2/en/manual/introduction/whatsnew620
• https://www.zabbix.com/rn/rn6.2.0

What is the replacement API?

The same deprecation warning is also in Host interface object documentation (https://www.zabbix.com/documentation/6.2/en/manual/api/reference/hostinterface/object) so it is not just the API that is deprecated but also the interface object itself (that is used by at least Host API).