Rooting is not necessary to install or use /e/OS on a device.
But for a device still maintained by the vendor (like the Pixel 5)
- to install /e/OS “R” build, you need to have android 11 gogol stock firmware installed as a base
- to install /e/OS “S” build, you need to have android 12 gogol stock firmware installed as a base
- to install /e/OS “T” build, you need to have android 13 gogol stock firmware installed as a base
For a device dropped by the vendor, you need latest available stock firmware as a base to install /e/ on it.