Self-scans reveal that Pegasus, an invasive and powerful spyware that can secretly control phones and track owners, might be more widespread than previously thought. It was discovered on the phones of everyday phone users.
From wikiHow: How to Check Your Smartphone for Pegasus Spyware
It can help you if you think you are BUT especially with iPhones it can only scan your backup, unless you jailbreak the phone and can do a full disk dump.
As a mobile security expert this is just one of the tools in the kit, but it ought not be used by a “end user” as a verification tool. This does NOT verify you aren’t being tracked, it can only verify that signatures of the malware exist.
And would signatures of Pegasus exist in the backup?
Yes. Maybe. Sometimes. Much more likely if you do an encrypted backup and decrypt it with the tool.
Regardless it’s not guaranteed to pick them up.
May give it a try one of these days. But knowing nothing of the reliability of the tool in detecting the malware decreases my motivation to even try I must say.
The warning was meant for you.