TheMrDec Is it possible to root, backup, and then unroot without seriously compromising device security and stability?
Though this is not recommended, some people do their own personal signed builds in pairs, with one build in each pair being rooted and the other not. Then it is possible to flash the rooted build (via OTA in Recovery), do whatever, then flash back the regular build. Of course, if anybody gains access to the signed rooted build image, they might be able to extract your data.
The officially supported backup approach is SeedVault, but it is imperfect, so many people manually back up data from various apps whether or not they use SeedVault.
Note that if your existing Pixel devices were obtained from Verizon, or were shipped as Verizon variants, it will be impossible to enable OEM unlocking and thus impossible to install GrapheneOS (or any non-Verizon OS image).