ROM basically is just another word for operating system so its about the software not the hardware. So only devices (phones) that allow you to install your own custom operating system (like a modified version of the original android that comes with it or even a proper linux OS) will allow you to install apps not certified by google.
Most of the time people talk about custom roms they mean open source software that replaces the pre installed closed source software. Nothing phones are closed source so they are probably not on the “good” side here.
ROM basically is just another word for operating system so its about the software not the hardware. So only devices (phones) that allow you to install your own custom operating system (like a modified version of the original android that comes with it or even a proper linux OS) will allow you to install apps not certified by google.
Most of the time people talk about custom roms they mean open source software that replaces the pre installed closed source software. Nothing phones are closed source so they are probably not on the “good” side here.