Well the one I’m thinking of, it had something like a 64x128 monochrome OLED screen, that fits the description of “surprisingly high resolution” for a pregnancy tester, but Doom would still appear as a “Pixelated screen” like you described. Its probably the same one we both saw. Either way, there is no microcontroller inside that device capable of running Doom, so an additional external microcontroller was attached to run the game itself.