AGiftFromGod
"I'm confused I had to download a app just to get redirected to this page."
Where did you download this application, could you link wherever you found it? GrapheneOS is not an application. Whatever you downloaded could be malicious and probably should be deleted.
Pegasus is, from my understand, an attack vector that primarily effects how iOS handles PDF files. I believe its patched by now, but was sold by an Israeli cyber-arms company NSO Group for military use. It was mainly used to target high profile individuals and was fairly expensive. You aren't effected by Pegasus.
Again, please delete any applications you installed on your cellphone and link where you found them. GOS is an operating system, based on the android project, thats only for Google Pixel phones. It's not an android application/APK file and anyone trying to have you install an APK onto your cellphone is doing something malicious.
Please read what Overlay1404 has linked, https://grapheneos.org/install/ has what you want. Also read https://grapheneos.org/faq