They haven’t said that Pixels won’t be supported.

The sideloading block will likely be enforced by Play Services, so GrapheneOS won’t be affected. Android is also open source, so even if Google implements the block within Android itself, GrapheneOS can just remove it.

GrapheneOS supports F-droid and essentially all APK files. The built in camera and SMS apps work and so do most IM apps and web browsers.

Ad networks have things like DoubleVerify, Human and Integral which can detect this, and it can cause account bans and captchas as well.

You should try GrapheneOS. It has no Google crap installed by default, and if you install Play Services for apps that need it, it will be sandboxed so it can’t track you or limit sideloading.