Which component of NGFW is supported in active/passive design but not in active/active design?

Single floating IP address (also known as a floating IP or shared IP) is supported only in an active/passive HA pair. In active/active HA, both firewalls are forwarding traffic simultaneously and thus do not share a single floating IP.

“In active/passive HA, a single floating IP address is used for seamless failover. Active/active HA requires separate IP addresses and does not support a single floating IP.”

(Source: Active/Passive vs. Active/Active HA)

This simplifies failover in active/passive deployments by using a single shared IP that moves to the active peer upon failover.