If anything, installing GrapheneOS on a Pixel probably reduces the risk of something happening to your phone, that's kind of the point with having an Android distribution that maximizes security and privacy.
And because the installer is so simple that you just connect your phone, open a browser and hit three buttons, it's really unlikely that you'll accidentally brick your phone trying to install it.
use Tor Browser.
If your concern is fingerprinting, that is undeniably the best there is out of the box.
If you want Tor Browser without having to use the Tor Network, Mullvad is basically just that; Tor Browser without the Network.