https://grapheneos.org/faq#recommended-devices
Edit: Also, Pixel 4's and under are EOL so you won't be able to install Graphene on them
The following devices are end-of-life, no longer receive firmware or driver security updates and receive extended support from GrapheneOS via a legacy branch based on Android 13 with only the Android Open Source Project security backports, certain other security patches and other minimal changes to keep them working:
Pixel 4a (sunfish)
Pixel 4 XL (coral)
Pixel 4 (flame)