What do you mean? The OP said that this is how Pegasus pwned (notice the past tense) the iPhone. That's correct. Moreover while Apple might have closed that specific vulnerability, would you bet your money (or even your live) on there not being other vulnerabilities in the apple indexer?
how can you be so confident that it's "closed"? the last time apple announced the high protection mode for state sponsored targets in new ios (whatever it's called), they disable all auto previews in that mode. if they are as confident as you are that it's "closed" that doesn't seem necessary?
Disabling link previews in high protection mode is more likely to be a combination of not issuing any network requests that could accidentally leak your IP, and being able to see the full URL so link previews can't pretend to be a different site to trick you into clicking on it.