GrapheneOS only supports Pixels due to their having superior security features [0]. Calyx supports Pixels as well as some newer Motos and the Fairphone 4 and 5 [1]. Lineage supports tons of devices [2].

LineageOS is the only one of the three that supports older hardware, but I'd recommend getting a previous-gen Pixel for the seven-year (at least) support cycle.

[0] https://grapheneos.org/faq#supported-devices

[1] https://calyxos.org/docs/guide/device-support/

[2] https://wiki.lineageos.org/devices/