AFAIK the Pixel devices are the only ones that reliably allow bootloader unlocking / re-locking, that is required to perform custom os installs.

There are others e.g. Motorola ones or Fairphone, that also allow this but it's a good idea to focus on a specific set of devices keeping maintenance as low as possible and security focus as high as possible.

There are alternatives like /eOS/ or CalyxOS supporting more devices and I experienced exactly this "no longer supported" issue with my Xiaomi A2, which suddenly disappeared from the list of supported devices (see https://calyxos.org/news/2021/03/29/mi-a2-ten-firmware/).

Pixels are the most secure Android devices and the only ones meeting the hardware security requirements for GrapheneOS at this time. GrapheneOS is working with a major Android OEM towards their future devices meeting these requirements.

Neither /e/ or CalyxOS is a hardened OS. They provide much weaker protection against these attacks than the stock Pixel OS or especially an iPhone. They're weakening privacy and security substantially including lagging many months and even years behind on standard security patches. CalyxOS has not shipped the June 2025-06-05 patch level or later. /e/ is regularly many months behind on OS and browser security patches along with very often being a year or more behind on kernel updates and firmware/driver updates.

See https://discuss.grapheneos.org/d/24134-devices-lacking-stand... with in-depth information about /e/ on Fairphone devices with links to multiple articles from third party security researchers covering it and other information.

Those non--Pixel devices do not provide a secure base either.