There are multiple steps in the exploit chain. It consists of seven different vulnerabilities (six of which need to be used).
Any version of iOS above 18.6 has the first step in the chain patched. So until an alternative exploit is found, those users are (just barely) safe.
Two other steps in the chain are patched for all releases above 18.7.2. The other four are patched in either 18.7.3 or 26.3.
Apple has made a decision that phones that support iOS 26 will no longer receive iOS 18 security patches past 18.7.2. Users on that version are safe for now, as they are protected against three of the seven vulnerabilities. However, they are still technically vulnerable to the other four CVEs (patched in 18.7.3 and 26.3), which could be used in concert with other exploit chains in the future.
Basically, if you care about security, and can run iOS 26, upgrading to that is the best course of action. Otherwise, if you're running an XS or XR, iOS 18.7.6 offers good protection against all but one of the CVEs. But if you're on a newer phone, and still on iOS 18, you're taking a risk by staying on iOS 18.7.2, which lacks the latest security patches.