Yes, since only Pixels allow secure verified boot for third party OS's. Basically Pixels let you run custom Android with a locked bootloader.
You can get unsupported third party GrapheneOS builds for other Android phones on sites like XDA but they won't actually be as secure because of this. They're also unofficial forks, although they are usually open source, still personally I always buy Pixels so I can run proper GrapheneOS.
I will say as well, Pixels are genuinely good phones. At least five of my friends switched to Pixels from other Android phones and they all love em.
