GrapheneOS only has support for OEM unlocked Google Pixel phones, and it runs pretty much perfectly on every device it supports. It is extremely easy to install, no rooting required. You just click buttons in a web browser while your phone is plugged in and there’s pretty much 0% chance of breaking anything.
You’re supposed to buy a phone specifically to run GrapheneOS. This isn’t a ROM that you can swap onto any device, it’s native to a specific platform. Also, using GrapheneOS does NOT void the warranty, you can always switch back to stock Android with Google’s web installer.