> My Google Pixel continuously asks me if I want to enable photo backup.

Google Photos does this on non-Pixel android phones too. Many times when I open the gallery app I'm confronted with a dialog where the backup checkbox is enabled and there's a continue button. It's like Google is trying to trick me into enabling it. This is an incredibly user hostile design. One day I will do it by mistake.

I mentioned this to a friend once and he said his kid got ahold of his phone for a few minutes and did enable it, causing a massive upload that put his Google account over quota. Of course it's a huge hassle to go through and unsync the photos without deleting them from the device.