Default OSs are very invasive. Windows, Mac and iOS are constantly spying on everything you do and stock Android is only as private as the apps it comes with which include things like Google Play Services - an app so baked into the system it can only be disabled through adb/root

If you want to read into this - Louis Rossmann made a video on this and this is the paper he mentioned.

possible for the average person who doesn't feel comfortable messing with installing operating systems to have any privacy?

Yes, depends on how far you are willing to take it.

Replace default apps with FOSS (F-droid)

Delete or disable defaut apps through developer options/adb

Limit the number of permissions you give to apps (your calculator shouldn't have access to internet or your camera)

Don't install apps that you don't trust/need

Block app's access to the internet with a firewall

Check out r/degoogle on Reddit for many useful resources

For Windows/iOS, etc.: change settings to be more private: give less permissions and turn off telemetry wherever possible.

If you think that's not enough, consider dual booting a Linux distro like Linux Mint Cinnamon (easy to set up and very beginer-friendly). If you do that you can learn Linux and keep your private data there instead of on Windows/iOS