> Unfortunately this is the case with most Android phones, aside from the Google Pixel series, which allow custom versions of Android, like open-source Graphene

> Unfortunately this is the case with most Android phones, aside from the Google Pixel series, which allow custom versions of Android, like open-source GrapheneOS, to be installed. In my experience, what's important is not the manufacturer of the phone, but whether or not the phone was bought from the carrier or the original manufacturer. If you buy a Pixel directly from Google, then the bootloader will be unlocked allowing you to install a different OS. If you buy the phone from a carrier like Verizon or At&t, the bootloader will be locked and it will be impossible to install a different OS.